Support the Arctic Sea Ice Forum and Blog

Author Topic: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE  (Read 421054 times)

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3650 on: August 16, 2020, 07:50:49 PM »
Maybe information entropy modeling methodology should be used in ESMs as it seems to improve ENSO forecasts as discussed in the linked reference:

Jun Meng et al. (January 7, 2020), "Complexity-based approach for El Niño magnitude forecasting before the spring predictability barrier", PNAS, 117 (1) 177- 183,  https://doi.org/10.1073/pnas.1917007117

https://www.pnas.org/content/117/1/177

Abstract: "Although El Niño events characterized by anomalous episodic warmings of the eastern equatorial Pacific can trigger disasters in various parts of the globe, reliable forecasts of their magnitude are still limited to about 6 mo ahead. A significant extension of this prewarning time would be instrumental for mitigating some of the worst damages. Here we introduce an approach relying on information entropy, which achieves some doubling of the prewarning time. The approach is based on our finding that the entropy in one calendar year exhibits a strong correlation with the magnitude of an El Niño that starts in the following year and thus allows us to forecast the onset and the magnitude of an El Niño event 1 y in advance."

...

A common adage in science is that: 'one man's noise is another man's signal'; thus, consensus climate science uses ensembles of forcing scenarios and ensembles of climate models (like CMIP) to average out variability to evaluate long-term climate trends.  Unfortunately, this consensus approach 'dumbs-down' possible signals from fat-tail climate risks particularly those associated with deep-uncertainty (such as: freshwater hosing events, aerosol feedback mechanisms and positive cloud feedback mechanisms).  Thus, I recommend that consensus climate scientists make more use of the concept of information entropy to better understand paleo, observed and model-projected date to better understand fat-tail climate risks (see the quoted reference which applied the concept of information entropy to get a better signal for ENSO projections and also I note that information entropy has been applied to better understand paleo-output from analyzing ice cores from Antarctica).

In this regard, the linked reference applies the concept of information entropy to better assess observed satellite data of SW and LW radiation measurements to highlight that cloud behavior/response represents a clear climate change risk in coming decades:

Delgado-Bonal, A., Marshak, A., Yang, Y. et al. Analyzing changes in the complexity of climate in the last four decades using MERRA-2 radiation data. Sci Rep 10, 922 (2020). https://doi.org/10.1038/s41598-020-57917-8

https://www.nature.com/articles/s41598-020-57917-8#citeas

Abstract: "The energy balance of the Earth is controlled by the shortwave and longwave radiation emitted to space. Changes in the thermodynamic state of the system over time affect climate and are noticeable when viewing the system as a whole. In this paper, we study the changes in the complexity of climate in the last four decades using data from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). First, we study the complexity of the shortwave and longwave radiation fields independently using Approximate Entropy and Sample Entropy, observing that the rate of complexity change is faster for shortwave radiation. Then, we study the causality of those changes using Transfer Entropy to capture the non-linear dynamics of climate, showing that the changes are mainly driven by the variations in shortwave radiation. The observed behavior of climatic complexity could be explained by the changes in cloud amount, and we research that possibility by investigating its evolution from a complexity perspective using data from the International Satellite Cloud Climatology Project (ISCCP)."

Extract: "In Information Theory, entropy is a magnitude which quantifies the information content in a data series.

Our research supports the idea that clouds and albedo, which ultimately determine the SW radiation, are variables of the utmost importance for current climate change, in agreement with previous research about the changes in stratocumulus or energy imbalance in the last four decades for example. An increase in cloud coverage of 0.1 would, on average, lead to a 7% increase in spectrally integrated global average reflectance of shortwave radiation55. The Decadal Survey for Earth Science and Applications from Space (2018) lists as one of the key science questions “how changing cloud cover and precipitation will affect climate, weather and Earth’s energy balance in the future”. We investigated the hypothesis that changes in clouds are responsible for the changes in SW radiation by calculating the evolution of complexity of cloud amount using ISCCP data, showing an increase in predictability and lower ApEn values, similarly to SW radiation. Even though the hypothesis of variations in cloud amount could explain the changes in SW radiation and the changes observed in the Transfer Entropy analysis, it is not possible to guarantee that clouds are the only factor since climate is a highly interconnected system, as reflected in the complexity of General Circulation Models."

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3651 on: August 16, 2020, 08:43:23 PM »
At over 70-pages of main text, it is not possible to summarize the content of the linked pdf on: "The Physics of Climate Variability and Climate Change".  Nevertheless, I note that the first part of the paper provides a nice overview of the consensus climate approach to projecting future climate change; while the second half of the paper provides a nice overview of some of the numerous shortcoming of the consensus climate science approach and discusses several 'dynamical systems theory' approaches to potential address some of the consensus climate science's shortcoming on addressing climate risk w.r.t non-equilibrium climate sensitivity.

Title: "The Physics of Climate Variability and Climate Change" by Michael Ghil, arXiv:1910.00583v2 [physics.ao-ph] 26 Feb 2020

https://arxiv.org/pdf/1910.00583.pdf

Abstract: "The climate system is a forced, dissipative, nonlinear, complex and heterogeneous system that is out of thermodynamic equilibrium. The system exhibits natural variability on many scales of motion, in time as well as space, and it is subject to various external forcings, natural as well as anthropogenic. This paper reviews the observational evidence on climate phenomena and the governing equations of planetary-scale flow, as well as presenting the key concept of a hierarchy of models as used in the climate sciences. Recent advances in the application of dynamical systems theory, on the one hand, and of nonequilibrium statistical physics, on the other, are brought together for the first time and shown to complement each other in helping understand and predict the system’s behavior. These complementary points of view permit a self-consistent handling of subgrid-scale phenomena as stochastic processes, as well as a unified handling of natural climate variability and forced climate change, along with a treatment of the crucial issues of climate sensitivity, response, and predictability."

Extract: "The ECS is widely considered to be the most important indicator in understanding climate response to natural and anthropogenic forcings. It is usually estimated from instrumental data coming from the industrial age, from proxy paleoclimatic data, and from climate models of different levels of complexity. In climate models, the ECS results from a nontrivial combination of several model parameters that enter the feedback factors {fk} in Eq. (45b) above, and it requires careful tuning. Despite many years of intense research, major uncertainties still exist in estimating it from past climatic data, as well as substantial discrepancies among different climate mode (IPCC, 2001, 2007, 2014a). In fact, Charney et al. (1979) estimated the ECS uncertainty as 1.5–4.5 K for CO2 doubling and this range of uncertainties has increased rather than decreased over the four intervening decades.

… it should be clear that the ECS is a state-dependent indicator.

Recently, Schneider et al. (2019), using very high-resolution simulations that represent explicitly convective processes, proposed a mechanism of instability of stratocumulus clouds occurring at high CO2 concentrations that greatly enhances the ECS and eventually leads to an abrupt transition to a much warmer climatic regime.

The standard viewpoint on climate sensitivity discussed above is associated with the idea that the climate is in equilibrium, in the absence of external perturbations.

But the internal climate variability can be better described in terms of strange attractors than by fixed points or limit cycles. Moreover, the presence of time-dependent forcing, deterministic as well as stochastic, introduces additional complexities into the proper definition of climate sensitivity. It is thus apparent that a rigorous definition of climate sensitivity requires considerably more effort.

The ECS concept is well suited for describing the properties of equilibrium solutions of heuristically simplified equations of the climate system, like Eq. 13a, and has clear intuitive appeal, as in Fig. 40a. But it also has basic scientific limitations:

• it only addresses long term-climatic changes and no detailed temporal information, an issue only partially addressed by TCR information;

• it only addresses changes in the globally averaged surface air temperature and no spatial information at the regional scale and at different levels of the atmosphere, of the ocean, and of the soil;

• it cannot discriminate between radiative forcings resulting from different physical and chemical processes, e.g. differences resulting from changes in aerosol vs. GHG concentration; the two impact quite differently shortwave and longwave radiation, and different atmospheric levels.

We will thus try to address these shortcomings by taking the complementary points of view of nonequilibrium statistical mechanics and dynamical systems theory. The setting of nonautonomous and of stochastically forced dynamical systems allows one to examine the interaction of internal climate variability with the forcing, whether natural or anthropogenic; it also helps provide a general definition of climate response that takes into account the climate system’s nonequilibrium behavior, its time-dependent forcing, and its spatial patterns.

Making these analogies stick at a level that might help determine more reliably climate sensitivity to human activities is clearly a worthwhile effort for the best mathematicians, physicists and climate scientists."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3652 on: August 17, 2020, 05:31:49 PM »
...
 (... and also I note that information entropy has been applied to better understand paleo-output from analyzing ice cores from Antarctica).

...

While the linked reference, and associated article, focus on the methodology of using permutation entropy to gain improved information about paleoclimate records, the findings of such studies can identify abrupt, decadal-scale, changes in the paleorecord.

Garland et al. (2018), "Anomaly Detection in Paleoclimate Records Using Permutation Entropy", Entropy 2018, 20(12), 931; https://doi.org/10.3390/e20120931

https://www.mdpi.com/1099-4300/20/12/931

Abstract: "Permutation entropy techniques can be useful for identifying anomalies in paleoclimate data records, including noise, outliers, and post-processing issues. We demonstrate this using weighted and unweighted permutation entropy with water-isotope records containing data from a deep polar ice core. In one region of these isotope records, our previous calculations (See Garland et al. 2018) revealed an abrupt change in the complexity of the traces: specifically, in the amount of new information that appeared at every time step. We conjectured that this effect was due to noise introduced by an older laboratory instrument. In this paper, we validate that conjecture by reanalyzing a section of the ice core using a more advanced version of the laboratory instrument. The anomalous noise levels are absent from the permutation entropy traces of the new data. In other sections of the core, we show that permutation entropy techniques can be used to identify anomalies in the data that are not associated with climatic or glaciological processes, but rather effects occurring during field work, laboratory analysis, or data post-processing. These examples make it clear that permutation entropy is a useful forensic tool for identifying sections of data that require targeted reanalysis—and can even be useful for guiding that analysis."

See also:

Title: "How complexity science can quickly detect climate record anomalies", 2018

https://www.santafe.edu/news-center/news/how-complexity-science-can-quickly-detect-anomalies-climate-records

Extract: "In previous cores, Garland notes that decades, even centuries, were aggregated into a single point. The WAIS data, by contrast, sometimes gives more than forty data points per year. But as scientists move to analyze the data at shorter time scales, even small anomalies can be problematic.

“As fine-grained data becomes available, fine-grained analyses can be performed,” Garland notes. “But it also makes the analysis susceptible to fine-grained anomalies.”

To quickly identify which anomalies require further investigation, the team uses information theoretic techniques to measure how much complexity appears at each point in the time sequence. A sudden spike in the complexity could mean that there was either a major, unexpected climate event, like a super volcano, or that there was an issue in the data or the data processing pipeline."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3653 on: August 17, 2020, 05:48:15 PM »
The linked reference indicates that the use of a dynamical framework can improve the interpretation of ancient SSTs; which, can help calibrate the fingerprint effect in modern ESM projections:

Emily J. Judd, Tripti Bhattacharya, Linda C. Ivany. A Dynamical Framework for Interpreting Ancient Sea Surface Temperatures. Geophysical Research Letters, 2020; 47 (15) DOI: 10.1029/2020GL089044

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GL089044

Abstract
Efforts to estimate past global mean temperature and latitudinal gradients must contend with spatial heterogeneity in sea surface temperatures (SSTs). Here, we use modern SSTs to show that the environments from which most paleoclimatic data are drawn, shallow epeiric seas and continental margins, are systematically offset from zonal mean temperatures. Epeiric seas are warmer and more seasonal than open‐ocean values from the same latitudes, while continental margins exhibit consistent and predictable deviations related to gyre circulation. Warm temperatures inferred from Paleozoic proxy data may largely reflect that these data derive almost entirely from epeiric seas. Moreover, pseudoproxy analysis using Paleogene sampling localities demonstrates how under-sampling of the full range of dynamical environments associated with gyre circulation can generate spurious estimates of latitudinal temperature gradients. Recognition of these global patterns permits a predictive framework within which to more robustly interpret proxy data, improve Earth system models, and reconstruct ancient dynamic regimes.

Plain Language Summary
Geochemical analyses provide estimates of past sea surface temperature. These data are integral to calculating global climate metrics, such as the latitudinal temperature gradient. For myriad reasons, the sites of these data are not evenly distributed across the global oceans but, instead, are biased toward two environments—continental margins and shallow continental seas. It is therefore important to determine the extent to which theses environments reflect broader climatic conditions. We use global ocean data to demonstrate that modern shallow, restricted seas are consistently warmer and more seasonal than anticipated for their given latitude. Because all sea surface temperature data older than ~200 Ma come from these environments, this observation could help explain why many Paleozoic temperatures appear unrealistically hot. Similarly, nearshore environments exhibit consistent offsets from the open ocean, both in terms of annual temperature and seasonal range, depending on their position within a gyre. This observation helps explain some of the longitudinal heterogeneity in paleoclimate data and should be used to inform locations to target for future data collection. Ignoring environment‐specific patterns can lead to spurious estimates of global climate metrics. However, cognizance of and correction for sampling location biases can improve interpretations of ancient climates.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

gerontocrat

  • First-year ice
  • Posts: 9328
    • View Profile
  • Liked: 3727
  • Likes Given: 28
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3654 on: August 17, 2020, 06:14:52 PM »
We should all remember that the fact that Antarctic sea ice extents have recently been, and currently are, higher than projected by CMIP6, this actual relatively high sea ice extent has been, and still is, promoting the upwelling of warm CDW; however, as indicated by the attached image, if the Antarctic sea ice extent actually decreases by 2035, the relative freshening of the Southern Ocean surface water will still continue to promote accelerated upwelling of warm CDW even with markedly reduced sea ice extent.
My pure speculation is that on the one hand "freshwater hosing" will increase not just from upwelling of CDW melting from beneath but also from increased surface melt as evidenced during the last Austral summer. But on the other hand, there is AGW, ocean heat gains, plus the acceleration of circumpolar currents pushing them southwards. Increasing cold & sea ice from the south meets increasing warmth from the north?

A reduced sea ice maximum extent but with thicker sea ice closer to the Antarctic continent, (and even wilder weather at the margin)?


"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
"Damn, I wanted to see what happened next" (Epitaph)

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3655 on: August 17, 2020, 07:09:06 PM »
We should all remember that the fact that Antarctic sea ice extents have recently been, and currently are, higher than projected by CMIP6, this actual relatively high sea ice extent has been, and still is, promoting the upwelling of warm CDW; however, as indicated by the attached image, if the Antarctic sea ice extent actually decreases by 2035, the relative freshening of the Southern Ocean surface water will still continue to promote accelerated upwelling of warm CDW even with markedly reduced sea ice extent.
My pure speculation is that on the one hand "freshwater hosing" will increase not just from upwelling of CDW melting from beneath but also from increased surface melt as evidenced during the last Austral summer. But on the other hand, there is AGW, ocean heat gains, plus the acceleration of circumpolar currents pushing them southwards. Increasing cold & sea ice from the south meets increasing warmth from the north?

A reduced sea ice maximum extent but with thicker sea ice closer to the Antarctic continent, (and even wilder weather at the margin)?

The first attached image provides an overview of some significant mechanisms associated with Antarctic sea ice (which points-out that the difference between precipitation and evaporation into/out of the Southern Ocean is important).

The second attached image shows the measured ocean heat content in the 0-2000m range through June 2020, showing that the ocean continuous to warm (& note that this record shows that the 'faux hiatus' was not a real pause).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3656 on: August 18, 2020, 04:32:41 PM »
The first image shows a compilation of worldwide tropical cyclone/hurricane tracks by NASA through 2006; while the second image shows similar tracks for the North Atlantic from 1851 thru 2019; which shows that since 2006 North Atlantic hurricanes have been penetrating deeper into the Arctic region.  Given James Hansen's warnings in "Storms of my Grandchildren", I wonder about:

a) How much heat energy such future storms will telecommunicate poleward from the tropics (especially as the MOC slows down),

b) Whether a future strong North Atlantic hurricane could penetrate deeply enough into to the Barents Sea (say by 2035) with sufficient strength to trigger a reversal of the Beaufort Gyre, and

c) Future North Atlantic hurricanes may increase rainfall over the GIS, permafrost regions and Arctic sea ice.

Edit, see also, the linked video indicating that we are already seeing an increased frequency of intensity hurricanes:

« Last Edit: August 18, 2020, 07:21:55 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3657 on: August 18, 2020, 08:13:31 PM »
The linked article discusses recent findings that the recent grounding line retreat of marine terminating glaciers in Greenland has resulted in a net ice mass loss for the GIS and that such grounding line retreats will likely go on for centuries.  While it is interesting to think about net ice mass loss from the GIS with time; to me this discuss ignores the influence of freshwater hosing from the marine terminating glacier discharges combined with the seasonal surface ice mass loss on the AMOC (i.e. causing the AMOC to slow).  As an acceleration of the slowing of the AMOC would increase TCR, I believe that most consensus climate model (including most CMIP6 model) projections are underestimating TCR this century:

Title: "Quantifying the impact of retreating glaciers on Greenland ice loss"

https://sustainabilitycommunity.springernature.com/posts/the-role-of-greenland-glaciers

Extract: "Large outlet glaciers in Greenland are changing rapidly. New analyses of over three decades of satellite data reveal that glaciers are draining more ice due almost entirely to observed retreat, with important implications for net ice sheet mass loss.

Further, many large glaciers are vulnerable to continued retreat, and modeling work suggests glacier discharge will remain a significant contributor to mass loss in the coming centuries. How rapidly these changes occur, however, is dependent on rates of atmospheric and oceanic warming."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3658 on: August 18, 2020, 08:53:42 PM »
The linked reference provides more details to the complex relationship between freshwater hosing in the North Atlantic and its impact on the AMOC:

Chengfei He et al. (1 June 2020), "North Atlantic subsurface temperature response controlled by effective freshwater input in “Heinrich” events", Earth and Planetary Science Letters, Volume 539, 116247, https://doi.org/10.1016/j.epsl.2020.116247

https://www.sciencedirect.com/science/article/pii/S0012821X20301904

Abstract
The northern North Atlantic (NNA) subsurface temperature in response to the slowdown of the Atlantic meridional overturning circulation (AMOC) is crucial for ice sheet calving and recovery of the AMOC in Heinrich events. Paleoclimate proxies and modeling studies suggest that the NNA subsurface exhibits a robust warming during Heinrich 1, but with a less clear response during Younger Dryas (YD). The mechanism for the potentially different subsurface responses has remained not well understood. Previous studies show different NNA subsurface response depending on hosing at different locations. Here, by examining a suite of “water-hosing” experiments with different hosing regions and intensities, we show that, regardless of the hosing location, NNA subsurface temperature response is determined by the effective freshening over the NNA deep convective regions through the competition between the warming associated with the suppressed vertical mixing and the cooling associated with the weakened AMOC heat transport. A weak effective freshening favors advective effect and, in turn, cooling, while a strong effective freshening strengthens the mixing effect and leads to a warming. Our results suggest that a cooling may occur in the NNA subsurface during YD.

Extract: "To summarize, our study quantitatively shows that the response of NNA subsurface temperature during Heinrich events is a result of the competition of local mixing associated with deep convection and advection associated with the AMOC. The sign and magnitude of the subsurface temperature depend on the effective freshening over the deep convection region, rather than where the freshwater is discharged as speculated in previous studies. A weak effective freshening favors the advective effect and causes subsurface cooling, while a strong effective freshening favors the mixing effect and generates subsurface warming.

It has been suggested that the greenhouse gas forcing may shallow the mixing layer and shut off the AMOC through air-sea surface heat flux exchange (Liu et al., 2017; Gregory et al., 2005), thus the nonlinear relationship between mixing and the AMOC under anthropogenic warming is also a way worthy to be explored."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3659 on: August 18, 2020, 10:15:15 PM »
The linked open access reference provides paleoclimate evidence that freshwater hosing events (particularly in the northern North Atlantic) has triggered abrupt climate change in the past and may do so again in the future:

Gerrit Lohmann et al., (10 August 2020), "Abrupt climate and weather changes across time scales", Paleoceanography and Paleoclimatology, https://doi.org/10.1029/2019PA003782

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019PA003782

abstract
The past provides evidence of abrupt climate shifts and changes in the frequency of climate and weather extremes. We explore the non‐linear response to orbital forcing and then consider climate millennial variability down to daily weather events. Orbital changes are translated into regional responses in temperature, where the precessional response is related to nonlinearities and seasonal biases in the system. We question regularities found in climate events by analyzing the distribution of inter‐event waiting times. Periodicities of about 900 and 1150 years are found in ice cores besides the prominent 1500‐years cycle. However, the variability remains indistinguishable from a random process, suggesting that centennial‐to‐millennial variability is stochastic in nature. New numerical techniques are developed allowing for a high resolution in the dynamically relevant regions like coasts, major upwelling regions, and high latitudes. Using this model, we find a strong sensitivity of the Atlantic meridional overturning circulation depending on where the deglacial meltwater is injected into. Meltwater into the Mississippi and near Labrador hardly affect the large‐scale ocean circulation, whereas subpolar hosing mimicking icebergs yields a quasi shutdown. The same multi‐scale approach is applied to radiocarbon simulations enabling a dynamical interpretation of marine sediment cores. Finally, abrupt climate events also have counterparts in the recent climate records, revealing a close link between climate variability, the statistics of North Atlantic weather patterns, and extreme events.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3660 on: August 19, 2020, 05:00:49 PM »
The linked reference provides an overview of literature findings on extreme weather and climate events in northern areas; which, provides useful background, but unfortunately does not focus on long-tail climate risks this century:

John E. Walsh et al. (2020), "Extreme weather and climate events in northern areas: A review", Earth-Science Reviews, https://doi.org/10.1016/j.earscirev.2020.103324

https://www.sciencedirect.com/science/article/pii/S0012825220303706?dgcid=rss_sd_all

Abstract
The greatest impacts of climate change on ecosystems, wildlife and humans often arise from extreme events rather than changes in climatic means. Northern high latitudes, including the Arctic, experience a variety of climate-related extreme events, yet there has been little attempt to synthesize information on extreme events in this region. This review surveys work on various types of extreme events in northern high latitudes, addressing (1) the evidence for variations and changes based on analyses of recent historical data and (2) projected changes based primarily on studies utilizing global climate models. The survey of extreme weather and climate events includes temperature, precipitation, snow, freezing rain, atmospheric blocking, cyclones, and wind. The survey also includes cryospheric and biophysical impacts: sea ice rapid loss events, Greenland Ice Sheet melt, floods, drought, wildfire, coastal erosion, terrestrial ecosystems, and marine ecosystems. Temperature and sea ice rank at the high end of the spectra of evidence for change and confidence in future change, while drought, flooding and cyclones rank at the lower end. Research priorities identified on the basis of this review include greater use of high-resolution models and observing system enhancements that target extreme events. There is also a need for further work on attribution, impacts on ecosystems and humans, and thresholds or tipping points that may be triggered by extreme events in high latitudes.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3661 on: August 19, 2020, 05:33:26 PM »
The linked reference presents findings on effective radiative forcing from 17 CMIP6 models and it finds that the CMIP6 models did not use particularly negative radiative forcing associated with aerosols and that the climate sensitivity values reported by the CMIP6 models (including the Wolf Pack values) were determined independently of the assumed aerosol forcings as indicated by the following extract:

"Therefore, there is no evidence to suggest that the increasing spread in climate sensitivity in CMIP6 models, particularly related to high-sensitivity models, is a consequence of a stronger negative present-day aerosol forcing and little evidence that modelling groups are systematically tuning climate sensitivity or aerosol forcing to recreate observed historical warming."

Smith, C. J., Kramer, R. J., Myhre, G., Alterskjær, K., Collins, W., Sima, A., Boucher, O., Dufresne, J.-L., Nabat, P., Michou, M., Yukimoto, S., Cole, J., Paynter, D., Shiogama, H., O'Connor, F. M., Robertson, E., Wiltshire, A., Andrews, T., Hannay, C., Miller, R., Nazarenko, L., Kirkevåg, A., Olivié, D., Fiedler, S., Lewinschal, A., Mackallah, C., Dix, M., Pincus, R., and Forster, P. M.: Effective radiative forcing and adjustments in CMIP6 models, Atmos. Chem. Phys., 20, 9591–9618, https://doi.org/10.5194/acp-20-9591-2020, 2020.

https://acp.copernicus.org/articles/20/9591/2020/
https://acp.copernicus.org/articles/20/9591/2020/acp-20-9591-2020.pdf

Abstract
The effective radiative forcing, which includes the instantaneous forcing plus adjustments from the atmosphere and surface, has emerged as the key metric of evaluating human and natural influence on the climate. We evaluate effective radiative forcing and adjustments in 17 contemporary climate models that are participating in the Coupled Model Intercomparison Project (CMIP6) and have contributed to the Radiative Forcing Model Intercomparison Project (RFMIP). Present-day (2014) global-mean anthropogenic forcing relative to pre-industrial (1850) levels from climate models stands at 2.00 (±0.23) W m−2, comprised of 1.81 (±0.09) W m−2 from CO2, 1.08 (± 0.21) W m−2 from other well-mixed greenhouse gases, −1.01 (± 0.23) W m−2 from aerosols and −0.09 (±0.13) W m−2 from land use change. Quoted uncertainties are 1 standard deviation across model best estimates, and 90 % confidence in the reported forcings, due to internal variability, is typically within 0.1 W m−2. The majority of the remaining 0.21 W m−2 is likely to be from ozone. In most cases, the largest contributors to the spread in effective radiative forcing (ERF) is from the instantaneous radiative forcing (IRF) and from cloud responses, particularly aerosol–cloud interactions to aerosol forcing. As determined in previous studies, cancellation of tropospheric and surface adjustments means that the stratospherically adjusted radiative forcing is approximately equal to ERF for greenhouse gas forcing but not for aerosols, and consequentially, not for the anthropogenic total. The spread of aerosol forcing ranges from −0.63 to −1.37 W m−2, exhibiting a less negative mean and narrower range compared to 10 CMIP5 models. The spread in 4×CO2 forcing has also narrowed in CMIP6 compared to 13 CMIP5 models. Aerosol forcing is uncorrelated with climate sensitivity. Therefore, there is no evidence to suggest that the increasing spread in climate sensitivity in CMIP6 models, particularly related to high-sensitivity models, is a consequence of a stronger negative present-day aerosol forcing and little evidence that modelling groups are systematically tuning climate sensitivity or aerosol forcing to recreate observed historical warming.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3662 on: August 19, 2020, 06:11:04 PM »
It is helpful to remember that the RCP scenarios use different atmospheric concentrations of GHGs; while the SSP scenarios use different emissions of GHGs.  Thus, the SSP scenarios used in CMIP6 can better evaluate pattern effects of precipitation and SST trends due to different emission patterns for both anthropogenic aerosols and GHGs; which the linked reference finds to be significant and which is one of the factors contributing to the different projections (including projections of climate sensitivity) found by CMIP5 and CMIP6:

Clara Deser et al. (2020), "Isolating the Evolving Contributions of Anthropogenic Aerosols and Greenhouse Gases: A New CESM1 Large Ensemble Community Resource", J. Climate, 33 (18): 7835–7858, https://doi.org/10.1175/JCLI-D-20-0123.1

https://journals.ametsoc.org/jcli/article/33/18/7835/353234/Isolating-the-Evolving-Contributions-of

Abstract
The evolving roles of anthropogenic aerosols (AER) and greenhouse gases (GHG) in driving large-scale patterns of precipitation and SST trends during 1920–2080 are studied using a new set of “all-but-one-forcing” initial-condition large ensembles (LEs) with the Community Earth System Model version 1 (CESM1), which complement the original “all-forcing” CESM1 LE (ALL). The large number of ensemble members (15–20) in each of the new LEs enables regional impacts of AER and GHG to be isolated from the noise of the model’s internal variability. Our analysis approach, based on running 50-yr trends, accommodates geographical and temporal changes in patterns of forcing and response. AER are shown to be the primary driver of large-scale patterns of externally forced trends in ALL before the late 1970s, and GHG to dominate thereafter. The AER and GHG forced trends are spatially distinct except during the 1970s transition phase when aerosol changes are mainly confined to lower latitudes. The transition phase is also characterized by a relative minimum in the amplitude of forced trend patterns in ALL, due to a combination of reduced AER and partially offsetting effects of AER and GHG. Internal variability greatly limits the detectability of AER- and GHG-forced trend patterns in individual realizations based on pattern correlation metrics, especially during the historical period, highlighting the need for LEs. We estimate that <20% of the spatial variances of observed precipitation and SST trends are attributable to AER and GHG forcing, although model biases in patterns of forced response and signal-to-noise may affect this estimate.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3663 on: August 19, 2020, 06:31:50 PM »
The linked reference uses regional Antarctic ice shelf basal melt rates perturbed by idealized (yet physically informed) trajectories as input to an MISI-type of model (CESMv2.1) in order to gain some insights into potential ranges of future sea level rise (assuming that MICI-type of mechanisms do not occur nor any bipolar seesaw mechanisms or and significant other freshwater hosing events like a reversal of the Beaufort Gyre and/or any cascades of tipping points).  Thus, in my opinion the presented SLR projections can be viewed as lower-bound possibilities.

Berdahl, M., Leguy, G., Lipscomb, W. H., and Urban, N. M.: Statistical emulation of a perturbed basal melt ensemble of an ice sheet model to better quantify Antarctic sea level rise uncertainties, The Cryosphere Discuss., https://doi.org/10.5194/tc-2020-178, in review, 2020.

https://tc.copernicus.org/preprints/tc-2020-178/
https://tc.copernicus.org/preprints/tc-2020-178/tc-2020-178.pdf

Abstract. Antarctic ice shelves are vulnerable to warming ocean temperatures, and have already begun thinning in response to increased basal melt rates. Sea level is therefore expected to rise due to Antarctic contributions, but uncertainties in its amount and timing remain largely unquantified. In particular, there is substantial uncertainty in future basal melt rates arising from multi-model differences in thermal forcing and how melt rates depend on that thermal forcing. To facilitate uncertainty quantification in sea level rise projections, we build, validate, and demonstrate projections from a computationally efficient statistical emulator of a high resolution (4 km) Antarctic ice sheet model, the Community Ice Sheet Model version 2.1. The emulator is trained to a large (500-member) ensemble of 200-year-long 4-km resolution transient ice sheet simulations, whereby regional basal melt rates are perturbed by idealized (yet physically informed) trajectories. The main advantage of our emulation approach is that by sampling a wide range of possible basal melt trajectories, the emulator can be used to (1) produce probabilistic sea level rise projections over much larger Monte Carlo ensembles than are possible by direct numerical simulation alone, thereby providing better statistical characterization of uncertainties, and (2) predict the simulated ice sheet response under differing assumptions about basal melt characteristics as new oceanographic studies are published, without having to run additional numerical ice sheet simulations. As a proof-of-concept, we propagate uncertainties about future basal melt rate trajectories, derived from regional ocean models, to generate probabilistic sea level rise estimates for 100 and 200 years into the future.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3664 on: August 19, 2020, 07:39:48 PM »
The linked pre-print discusses some of the mechanisms associated with low-frequency (decadal and longer timescales) variability of the AMOC and the North Atlantic Ocean heat transport.  I provided this information as it is important to appreciate how the AMOC functions without probable future significant freshwater hosing impacts (such as from a reversal of the Beaufort Gyre).

Oldenburg D, RCJ Wills, KC Armour and L Thompson (2020), "Mechanisms of low-frequency variability in North Atlantic Ocean heat transport and AMOC", Journal of Climate, pre-print.

http://faculty.washington.edu/karmour/papers/Oldenburg_JClimate2020_submitted.pdf

Abstract: "Northward ocean heat transport (OHT) plays a key role in climate and its variability. Here, we decompose OHT in the North Atlantic into modes of variability sorted by their dominant timescale by applying a low-frequency component analysis (LFCA) to output from three global climate models. The first low-frequency component (LFC), computed using this method, is an index of OHT variability that maximizes the ratio of low-frequency variance (occurring at decadal and longer timescales) to total variance. Lead-lag regressions of atmospheric and ocean variables onto the LFC timeseries illuminate the dominant mechanisms controlling low-frequency OHT variability. Anomalous northwesterly winds from eastern North America over the North Atlantic act to increase upper ocean density in the Labrador Sea region, enhancing deep convection, which later increases OHT via changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC). The strengthened AMOC carries warm, salty water into the subpolar gyre, reducing convection and weakening AMOC and OHT. This mechanism, where changes in AMOC and OHT are driven primarily by changes in Labrador Sea deep convection, holds not only in models where the climatological (i.e., time-mean) deep convection is concentrated in the Labrador Sea, but also in models where the climatological deep convection is concentrated in the Greenland-Iceland-Norwegian (GIN) Seas. These results suggest that despite recent observations suggesting that the Labrador Sea plays a minor role in driving climatological AMOC, the Labrador Sea may still play an important role in driving low-frequency AMOC and OHT variability."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3665 on: August 19, 2020, 07:50:05 PM »
The linked website provides a nice summary of the nature of the International Thwaites Glacier Collaboration (ITGC).

Title: "About the ITGC"

https://thwaitesglacier.org/about/itgc

Extract related to the attached image: "Thwaites Glacier (in darker blue) drains a vast part of the West Antarctic Ice Sheet, extending over 192,000 square kilometers, or 74,000 square miles—an area the size of Florida or the island of Britain. Each of the ITGC field projects, shown as red solid circles, has a principle geographic focus of their study, related to the processes they intend to study. The two modeling studies, PROPHET and DOMINOS are shown as open circles in orange. TIME is a study of how the boundary of the glacier evolves, and what the differences are between the slow-moving ice and underlying rock outside the glacier is versus the interior. GHOST is a traverse of the core of the glacier, looking at ice and bedrock characteristics with seismic and radar data. GHC will collect rock samples from either side of Thwaites Glacier to look for clues as to its recent past history—as will the THOR project, using marine sediments, bathymetric mapping, and oceanography. MELT and TARSAN both have a focus on the ice-ocean interaction at the point of contact between land, ice, and sea, looking at ocean circulation and rates of ice melt near the front of the glacier. SCO coordinates other projects."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

kassy

  • Nilas ice
  • Posts: 2466
    • View Profile
  • Liked: 1180
  • Likes Given: 1027
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3666 on: August 20, 2020, 03:19:07 PM »
Todays free bonus.  :)

Quote
Climate change: Dams played key role in limiting sea level rise

The construction of large-scale dams has played a surprising role in limiting rising seas, say scientists.

Over the past century, melting glaciers and the thermal expansion of sea water have driven up ocean levels.

But this new study finds that dams almost stalled the rising seas in the 1970s because of the amount of water they prevented from entering the oceans.

Without them, the annual rate of rise would have been around 12% higher.

...

There are around 58,000 large dams in the world right now with many of them constructed over the past 60 years.

The 1950s to 1970s saw a building boom with several large-scale constructions completed, including the Kariba Dam in Zimbabwe, the Bratsk Dam in Siberia and the Aswan High Dam in Egypt.

When the full impact of these giants came on stream in the 1970s, their ability to block water from going into the sea slowed the ongoing rise in global sea level.

"A large part of this dip is because sea level [rise] was almost brought to a halt because of the amount of water stored in dams," said lead author Dr Thomas Frederikse, from Nasa's Jet Propulsion Laboratory in Pasadena, California.

"So by building dams, we almost stopped sea level rise for a decade or so."

https://www.bbc.com/news/science-environment-53836018

https://www.nature.com/articles/s41586-020-2591-3
Þetta minnismerki er til vitnis um að við vitum hvað er að gerast og hvað þarf að gera. Aðeins þú veist hvort við gerðum eitthvað.

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3667 on: August 20, 2020, 05:09:08 PM »
The attached image was created by Dessler (adapted/updated from Hansen et al. 2012) showing the June-July-August seasonal average 30oN-60oN land temperatures for 1951-1980 (left plot) and for 2011-2020 (right plot).  To me this image helps to illustrate how climate change can transform a long-tail climate risk in one period into an average climate risk in another period, within just a few decades.  To me the lesson conveyed by this image is highly relevant to the current long-tail ice apocalypse risk; which may well become an average risk in the coming decades:

Extract:
"Andrew Dessler
@AndrewDessler

The left plot shows the 1951-1980 June-July-August seasonal average for northern hemisphere land (30°N-60°N). The blue area is the coolest is 33% of temperatures, the white area or the middle 33%, and the red or the highest 33%.

The right plot shows the 2011-2020 temperatures. Over the decade, 88% of the seasonal averages would have been in the top third in the 1951-1980 period. Only 1.2% would have been in the coolest third. And 14% are warmer than ANY temperatures in the 1951-1980 period."

Edit: For those who may think that I am mixing apples and oranges by comparing shifts in the June-July-August northern land temperatures with possible shifts in the probabilities of scenarios leading to a possible ice apocalypse this century, I note that  Roach et al. (17 April 2020) indicates that the Arctic Ocean may be seasonally ice free by 2035; while might be a sufficient perturbation to trigger a reversal of the Beaufort Gyre while might trigger an abrupt slowing of the AMOC that could be sufficient to trigger an ice apocalypse scenario.
« Last Edit: August 20, 2020, 07:15:45 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3668 on: August 20, 2020, 06:05:01 PM »
Todays free bonus.  :)

Quote
Climate change: Dams played key role in limiting sea level rise

...

Without them, the annual rate of rise would have been around 12% higher.

...

...

"A large part of this dip is because sea level [rise] was almost brought to a halt because of the amount of water stored in dams," said lead author Dr Thomas Frederikse, from Nasa's Jet Propulsion Laboratory in Pasadena, California.

"So by building dams, we almost stopped sea level rise for a decade or so."

https://www.bbc.com/news/science-environment-53836018

https://www.nature.com/articles/s41586-020-2591-3

As a service I provide the associated citation and abstract and I note that while it is nice to close the observed (since 1900) GMSLR budget, to me the presentation in this reference (see the attached image) of this findings obscures the risk of greatly accelerated GMSLR contributions from the WAIS this century:

Frederikse, T., Landerer, F., Caron, L. et al. The causes of sea-level rise since 1900. Nature 584, 393–397 (2020). https://doi.org/10.1038/s41586-020-2591-3

https://www.nature.com/articles/s41586-020-2591-3

Abstract
The rate of global-mean sea-level rise since 1900 has varied over time, but the contributing factors are still poorly understood. Previous assessments found that the summed contributions of ice-mass loss, terrestrial water storage and thermal expansion of the ocean could not be reconciled with observed changes in global-mean sea level, implying that changes in sea level or some contributions to those changes were poorly constrained. Recent improvements to observational data, our understanding of the main contributing processes to sea-level change and methods for estimating the individual contributions, mean another attempt at reconciliation is warranted. Here we present a probabilistic framework to reconstruct sea level since 1900 using independent observations and their inherent uncertainties. The sum of the contributions to sea-level change from thermal expansion of the ocean, ice-mass loss and changes in terrestrial water storage is consistent with the trends and multidecadal variability in observed sea level on both global and basin scales, which we reconstruct from tide-gauge records. Ice-mass loss—predominantly from glaciers—has caused twice as much sea-level rise since 1900 as has thermal expansion. Mass loss from glaciers and the Greenland Ice Sheet explains the high rates of global sea-level rise during the 1940s, while a sharp increase in water impoundment by artificial reservoirs is the main cause of the lower-than-average rates during the 1970s. The acceleration in sea-level rise since the 1970s is caused by the combination of thermal expansion of the ocean and increased ice-mass loss from Greenland. Our results reconcile the magnitude of observed global-mean sea-level rise since 1900 with estimates based on the underlying processes, implying that no additional processes are required to explain the observed changes in sea level since 1900.

Caption: "Fig. 1 | Observed GMSL and contributing processes. a, Observed GMSL, and the estimated barystatic and thermosteric contributions and their sum. b, The barystatic contribution and its individual components. The TWS term is the sum of groundwater depletion, water impoundment in artificial reservoirs and the natural TWS term. c, 30-year-average rates of observed GMSL change and of GMSL change as a result of the different contributing processes. d, 30-yearaverage rates of GMSL change due to the barystatic contribution and its individual components. The shaded regions denote 90% confidence intervals. The values in a and b are relative to the 2002–2018 mean"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3669 on: August 20, 2020, 06:25:30 PM »
While consensus climate sciences like to emphasize that collectively we still have time to avoid the worst impacts of mankind's global footprint; I note that each day that we exceed the planet's ability to replenish its natural resources (including carbon sinks; and which occurs on August 22nd this year) increases that probability of the occurrence of an ice apocalypse this century:

Title: "Humans overshoot 2020 planetary 'budget' on August 22: report"

https://phys.org/news/2020-08-humans-overshoot-planetary-august.html

Extract: "The group calculates the point will be reached on August 22, compared to July 29 in 2019, marking a rare reversal after lockdowns to slow the new coronavirus caused a temporary decline in emissions and wood harvesting.

Researchers calculate the date humanity overshoots its planetary budget by looking at "all the human demands" for food, energy, space for houses and roads and what would be needed to absorb global CO2 emissions, Wackernagel said.

Comparing that with what is sustainably available, they estimate that humanity is using 60 percent more than can be renewed—the equivalent of 1.6 planets."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Tom_Mazanec

  • Young ice
  • Posts: 3639
    • View Profile
    • Planet Mazanec
  • Liked: 625
  • Likes Given: 315
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3670 on: August 20, 2020, 06:47:50 PM »
Quote
But this new study finds that dams almost stalled the rising seas in the 1970s because of the amount of water they prevented from entering the oceans.

Without them, the annual rate of rise would have been around 12% higher.
Interesting that a 12% reduction is called "almost stalled".
And we've dammed all the "low hanging fruit".
SHARKS (CROSSED OUT) MONGEESE (SIC) WITH FRICKIN LASER BEAMS ATTACHED TO THEIR HEADS

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3671 on: August 20, 2020, 10:07:48 PM »
Quote
But this new study finds that dams almost stalled the rising seas in the 1970s because of the amount of water they prevented from entering the oceans.

Without them, the annual rate of rise would have been around 12% higher.
Interesting that a 12% reduction is called "almost stalled".
And we've dammed all the "low hanging fruit".

While; I have seen proposals to pump ocean water into basins in both the Sahara Desert and the Australian Outback in order to fight sea level rise; but aside from the high expense of such concepts they would do nothing to stop ice-climate feedback mechanisms such as the slowing of the MOC associated with freshwater hosing events and/or an albedo flip associated with a seasonal loss of the Arctic/Antarctic sea ice areas.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3672 on: August 20, 2020, 11:12:32 PM »
The linked reference concludes that:

"This study demonstrates substantial permafrost thaw from the projected increasing summer precipitation across most of the Arctic region."

This suggests that Arctic Amplification will likely increase more than previously projected by consensus climate science:

Thomas A. Douglas, Merritt R. Turetsky, Charles D. Koven. Increased rainfall stimulates permafrost thaw across a variety of Interior Alaskan boreal ecosystems. npj Climate and Atmospheric Science, 2020; 3 (1) DOI: 10.1038/s41612-020-0130-4

https://www.nature.com/articles/s41612-020-0130-4

Abstract: "Earth’s high latitudes are projected to experience warmer and wetter summers in the future but ramifications for soil thermal processes and permafrost thaw are poorly understood. Here we present 2750 end of summer thaw depths representing a range of vegetation characteristics in Interior Alaska measured over a 5 year period. This included the top and third wettest summers in the 91-year record and three summers with precipitation close to mean historical values. Increased rainfall led to deeper thaw across all sites with an increase of 0.7 ± 0.1 cm of thaw per cm of additional rain. Disturbed and wetland sites were the most vulnerable to rain-induced thaw with ~1 cm of surface thaw per additional 1 cm of rain. Permafrost in tussock tundra, mixed forest, and conifer forest was less sensitive to rain-induced thaw. A simple energy budget model yields seasonal thaw values smaller than the linear regression of our measurements but provides a first-order estimate of the role of rain-driven sensible heat fluxes in high-latitude terrestrial permafrost. This study demonstrates substantial permafrost thaw from the projected increasing summer precipitation across most of the Arctic region."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

vox_mundi

  • Young ice
  • Posts: 4107
    • View Profile
  • Liked: 2399
  • Likes Given: 318
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3673 on: August 21, 2020, 12:04:17 AM »
Larger Variability in Sea Level Expected as Earth Warms
https://phys.org/news/2020-08-larger-variability-sea-earth.html

A team of researchers from the University of Hawai'i (UH) at Mānoa School of Ocean and Earth Science and Technology (SOEST) identified a global tendency for future sea levels to become more variable as oceans warm this century due to increasing greenhouse gas emissions. Sea level variability alters tidal cycles and enhances the risks of coastal flooding and erosion beyond changes associated with sea level rise.

In a study published this week in Communications Earth & Environment, the team led by Matthew Widlansky, associate director of the UH Sea Level Center, assessed future sea level projections from global climate models. The team found that while future sea level variability changes are uncertain in many locations, nearly all of the 29 models they analyzed agreed on an overall tendency for the variability to increase on seasonal-to-interannual timescaled.

"Whereas it is well understood that the rate of global mean sea level rise will accelerate with future warming, in part due to the oceans expanding faster at higher temperatures, it was previously unexplored how this nonlinear thermal expansion property of seawater will affect future sea level variability," said Widlansky.


Future projection of changing sea level annual range with increasing greenhouse gas concentrations during the 21st century. The global tendency for increasing sea level variability is explained by the yearly range of seawater buoyancy becoming larger as the oceans warm. Climate models disagree about the future change in some regions (stippling) because of other contributing processes, such as changes in ocean temperature variability, which are more uncertain.

... In places where changes due to ocean thermodynamics and other climate variability processes align, the team found the largest increases in future sea level variability.

Coastal flooding occurs increasingly often due to a combination of slowly rising sea levels and ocean variability. The new findings therefore further emphasize the importance of sea level monitoring and forecasting.

Widlansky, M.J., Long, X. & Schloesser, F. Increase in sea level variability with ocean warming associated with the nonlinear thermal expansion of seawater. Commun Earth Environ 1, 9 (2020).
https://www.nature.com/articles/s43247-020-0008-8
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― Leonardo da Vinci

Insensible before the wave so soon released by callous fate. Affected most, they understand the least, and understanding, when it comes, invariably arrives too late

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3674 on: August 21, 2020, 12:40:32 AM »
Ice mass loss from Greenland reached an all time high in 2019; which contributes to a slowing of the AMOC:

Title: "Record melt: Greenland lost 586 billion tons of ice in 2019"

https://apnews.com/6fcaab97241d34c83f448f019179ca6b

Extract: "After two years when summer ice melt had been minimal, last summer shattered all records with 586 billion tons (532 billion metric tons) of ice melting, according to satellite measurements reported in a study Thursday. That’s more than 140 trillion gallons (532 trillion liters) of water.

That’s far more than the yearly average loss of 259 billion tons (235 billion metric tons) since 2003 and easily surpasses the old record of 511 billion tons (464 billion metric tons) in 2012, said a study in Communications Earth & Environment. The study showed that in the 20th century, there were many years when Greenland gained ice."

See also:

King, M.D., Howat, I.M., Candela, S.G. et al. Dynamic ice loss from the Greenland Ice Sheet driven by sustained glacier retreat. Commun Earth Environ 1, 1 (2020). https://doi.org/10.1038/s43247-020-0001-2

https://www.nature.com/articles/s43247-020-0001-2

Abstract: "The Greenland Ice Sheet is losing mass at accelerated rates in the 21st century, making it the largest single contributor to rising sea levels. Faster flow of outlet glaciers has substantially contributed to this loss, with the cause of speedup, and potential for future change, uncertain. Here we combine more than three decades of remotely sensed observational products of outlet glacier velocity, elevation, and front position changes over the full ice sheet. We compare decadal variability in discharge and calving front position and find that increased glacier discharge was due almost entirely to the retreat of glacier fronts, rather than inland ice sheet processes, with a remarkably consistent speedup of 4–5% per km of retreat across the ice sheet. We show that widespread retreat between 2000 and 2005 resulted in a step-increase in discharge and a switch to a new dynamic state of sustained mass loss that would persist even under a decline in surface melt."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3675 on: August 21, 2020, 06:20:38 PM »
The linked reference has T. Edwards as a co-author; and to me this reference illustrates how consensus climate scientist continue to err on the side of least drama (ESLD) regarding the actual risks of ice mass loss from the Amundsen Sea Embayment, ASE, marine glaciers in the next 50-years for reasons including:

- The authors assert that they use the most recent observational data available, which very clearly is not the case as illustrated by the attached image of their model's initial simulation of the ASE ice shelve, which are much more robust than the fragile condition that these ASE ice shelves are currently in.

- The is no modeling of the subglacial cavities in the gateway of the Thwaites Glacier that have been observed for well over two years now.

- The model assumes MISI behavior with no possibility of a transition from MISI behavior to MICI behavior.

- By ignoring paleodata, such as observed ice-rafted debris [see Smith et al. (2019)] which can only occur due to MICI behavior; the author show clear bias towards assuming that only MISI behavior can occur in the next 50-years.

Therefore, in my opinion this work can only be considered as projecting a lower bound to ASE contributions to SLR in the coming 50-years.

Wernecke, A., Edwards, T. L., Nias, I. J., Holden, P. B., and Edwards, N. R.: Spatial probabilistic calibration of a high-resolution Amundsen Sea Embayment ice sheet model with satellite altimeter data, The Cryosphere, 14, 1459–1474, https://doi.org/10.5194/tc-14-1459-2020, 2020.

https://tc.copernicus.org/articles/14/1459/2020/

Abstract
Probabilistic predictions of the sea level contribution from Antarctica often have large uncertainty intervals. Calibration of model simulations with observations can reduce uncertainties and improve confidence in projections, particularly if this exploits as much of the available information as possible (such as spatial characteristics), but the necessary statistical treatment is often challenging and can be computationally prohibitive. Ice sheet models with sufficient spatial resolution to resolve grounding line evolution are also computationally expensive.

Here we address these challenges by adopting and comparing dimension-reduced calibration approaches based on a principal component decomposition of the adaptive mesh model BISICLES. The effects model parameters have on these principal components are then gathered in statistical emulators to allow for smooth probability density estimates. With the help of a published perturbed parameter ice sheet model ensemble of the Amundsen Sea Embayment (ASE), we show how the use of principal components in combination with spatially resolved observations can improve probabilistic calibrations. In synthetic model experiments (calibrating the model with altered model results) we can identify the correct basal traction and ice viscosity scaling parameters as well as the bedrock map with spatial calibrations. In comparison a simpler calibration against an aggregated observation, the net sea level contribution, imposes only weaker constraints by allowing a wide range of basal traction and viscosity scaling factors.

Uncertainties in sea level rise contribution of 50-year simulations from the current state of the ASE can be reduced with satellite observations of recent ice thickness change by nearly 90 %; median and 90 % confidence intervals are 18.9 [13.9, 24.8] mm SLE (sea level equivalent) for the proposed spatial calibration approach, 16.8 [7.7, 25.6] mm SLE for the net sea level calibration and 23.1 [−8.4, 94.5] mm SLE for the uncalibrated ensemble. The spatial model behaviour is much more consistent with observations if, instead of Bedmap2, a modified bedrock topography is used that most notably removes a topographic rise near the initial grounding line of Pine Island Glacier.

The ASE dominates the current Antarctic sea level contribution, but other regions have the potential to become more important on centennial scales. These larger spatial and temporal scales would benefit even more from methods of fast but exhaustive model calibration. Applied to projections of the whole Antarctic ice sheet, our approach has therefore the potential to efficiently improve our understanding of model behaviour, as well as substantiating and reducing projection uncertainties.

For ice-rafted debris information see:

Smith, J.A., Graham, A.G.C., Post, A.L. et al. The marine geological imprint of Antarctic ice shelves. Nat Commun 10, 5635 (2019). https://doi.org/10.1038/s41467-019-13496-5

https://www.nature.com/articles/s41467-019-13496-5

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3676 on: August 21, 2020, 08:28:23 PM »
The linked reference discusses (among other evidence) ice rafted debris (IRD) evidence that for the last 2.5 million years that marine-termination ice sheets in Europe extended into the ocean to varying extents (with time).  Such IRD evidence confirms that these ice sheets (with marine-terminating glaciers) exhibited MICI behavior, such as may occur in the AIS in coming decades.

Brice R. Rea et al. (13 Jun 2018), "Extensive marine-terminating ice sheets in Europe from 2.5 million years ago", Science Advances, Vol. 4, no. 6, eaar8327, DOI: 10.1126/sciadv.aar8327

https://advances.sciencemag.org/content/4/6/eaar8327.full

Abstract
Geometries of Early Pleistocene [2.58 to 0.78 million years (Ma) ago] ice sheets in northwest Europe are poorly constrained but are required to improve our understanding of past ocean-atmosphere-cryosphere coupling. Ice sheets are believed to have changed in their response to orbital forcing, becoming, from about 1.2 Ma ago, volumetrically larger and longer-lived. We present a multiproxy data set for the North Sea, extending to over a kilometer below the present-day seafloor, which demonstrates spatially extensive glaciation of the basin from the earliest Pleistocene. Ice sheets repeatedly entered the North Sea, south of 60°N, in water depths of up to ~250 m from 2.53 Ma ago and subsequently grounded in the center of the basin, in deeper water, from 1.87 Ma ago. Despite lower global ice volumes, these ice sheets were near comparable in spatial extent to those of the Middle and Late Pleistocene but possibly thinner and moving over slippery (low basal resistance) beds.

Extract: "For the hypothesis to have validity, other Early Pleistocene ice sheets should also be spatially extensive. It has been demonstrated, using IRD, that marine-terminating ice masses were present on Greenland, Fennoscandia, and the British Isles from the end of the Pliocene (4–6) and in Siberia-Kamchatka and Alaska from the beginning of the Pleistocene (48, 49). To date, constraints on the geometries of any of these ice sheets have been missing, and the presence of distal IRD deposits provides only minimal constraint on ice geometries. Until now, the only supporting evidence of expanded Early Pleistocene ice cover came from the Cordilleran ice sheet (44) at 2.64 Ma ago. A regolith cover, similar to that hypothesized for the LIS, has long been known for NW Europe (34, 50, 51), but definitive evidence constraining the extent of Early Pleistocene ice sheets in this region was missing."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3677 on: August 22, 2020, 10:52:25 AM »
The linked reference associates Heinrich events and Dansgaard-Oeschger cycles (or events) can be related to MICI mechanisms:

Bassis, J., Petersen, S. & Mac Cathles, L. Heinrich events triggered by ocean forcing and modulated by isostatic adjustment. Nature 542, 332–334 (2017). https://doi.org/10.1038/nature21069

https://www.nature.com/articles/nature21069?WT.feed_name=subjects_geodynamics

Abstract: "During the last glacial period, the Laurentide Ice Sheet sporadically discharged huge numbers of icebergs through the Hudson Strait into the North Atlantic Ocean, leaving behind distinct layers of ice-rafted debris in the ocean sediments. Perplexingly, these massive discharge events—Heinrich events—occurred during the cold portion of millennial-scale climate oscillations called Dansgaard–Oeschger cycles. This is in contrast to the expectation that ice sheets expand in colder climates and shrink in warmer climates. Here we use an ice sheet model to show that the magnitude and timing of Heinrich events can be explained by the same processes that drive the retreat of modern marine-terminating glaciers. In our model, subsurface ocean warming associated with variations in the overturning circulation increases underwater melt along the calving face, triggering rapid margin retreat and increased iceberg discharge. On millennial timescales, isostatic adjustment causes the bed to uplift, isolating the terminus from subsurface warming and allowing the ice sheet to advance again until, at its most advanced position, it is poised for another Heinrich event. This mechanism not only explains the timing and magnitude of observed Heinrich events, but also suggests that ice sheets in contact with warming oceans may be vulnerable to catastrophic collapse even with little atmospheric warming."

Extract: "Given the lack of evidence for an ice shelf, a more relevant modern analogy comes from observations of widespread retreat of glaciers surrounding Greenland driven by the intrusion of warm subsurface ocean waters into fjords. We use both a width-averaged flowline and a regional ice sheet model of the Laurentide Ice Sheet and Hudson Strait Ice Stream to show that small increases in submarine melt at the calving terminus is limited by the strength of glacier ice, a theory proposed in refs 19 and 20 and called the “marine ice cliff instability”. This parameterization is calibrated to a wide variety of Greenland, Svalbard and Alaskan marine-terminating-glaciers (Supplementary Information, section 3.3). Isostatic adjustment of the bed, which is important on millennial timescales, is modelled as an elastic lithosphere overlying a viscous mantle with upper-mantle viscosity consistent with inferences based on Hudson Bay uplift data (Supplementary Information, section 3.6).

Researchers have struggled for decades to understand why the Laurentide Ice Sheet collapsed repeatedly during the cold intervals of the last glacial cycle. Our model solves this problem and shows that Heinrich events can be triggered by relatively small millennial-scale fluctuations in subsurface ocean temperature. This mechanism explains the observed abrupt collapse, long recovery and recurrence interval of Heinrich events, as well as the alignment between Heinrich events within the cold phases of Dansgaard–Oeschger events when atmospheric temperatures are coldest, without requiring an ice shelf. The presence of IRD from other ice sheets within Heinrich layers dominated by Hudson-Strait-derived IRD further strengthens our hypothesis, as it is likely that the basin-wide subsurface warming that triggers Heinrich events would also trigger other ice masses to release smaller amounts of IRD. The much smaller size of these other ice masses allows a more rapid recovery, making them more susceptible to ocean warming during non-Heinrich-event stadials, analogous to the increased calving flux associated with ocean-driven retreat of Greenland’s modern tidewater glaciers and as observed in the sediment record. Finally, observations from Greenland’s largest glaciers show that sediment-rich icebergs frequently capsize after detaching, providing a mechanism that allows icebergs to travel great distances before depositing their sediment load to form the Heinrich layers.

The mechanism we propose implies that Heinrich events are controlled by the same processes that drive retreat of modern marine-terminating glaciers, albeit on a much grander scale than is possible in the confines of Greenland’s smaller outlet glaciers. This suggests that portions of West Antarctica already at risk of collapse, like the Amundsen Sea Embayment, where wide ice streams are grounded deep beneath sea level, could be vulnerable to an ocean-triggered Heinrich-event-style demise, even in the absence of atmospheric warming."

For background information on Heinrich, and Dansgaard-Oeschger, events see the linked Wikipedia articles:

https://en.wikipedia.org/wiki/Dansgaard%E2%80%93Oeschger_event

https://en.wikipedia.org/wiki/Heinrich_event

https://en.wikipedia.org/wiki/Ice_rafting
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3678 on: August 22, 2020, 11:09:52 AM »
The linked reference "… indicates that the tides may serve as both a trigger and forcing for Heinrich events."  This is not good news, given that the recently reported subglacial cavities in the Thwaites Glacier gateway are currently being enlarged by tidal forcing.

Jesse Velay‐Vitow, W. Richard Peltier and Gordan R. Stuhne (12 January 2020), "The Tides of the Glacial Ocean and Their Possible Connection to Heinrich Event Instabilities of the Laurentide Ice Sheet", JGR Oceans, https://doi.org/10.1029/2019JC015444

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JC015444

Abstract
The possibility that Heinrich event 1 (H1), which occurred during the most recent deglaciation event of the current ice age, may have been both triggered and subsequently continuously forced by the tides, is investigated. For the purpose of this investigation, a discontinuous Galerkin method is employed to solve the shallow water tidal equations on the sphere using a nonuniform icosahedral grid to enable high resolution of the Hudson Strait region that was the locus of the ice stream instability that caused H1. Since Heinrich events are known to have involved, for most if not all such events, an instability of the Hudson Strait Ice Stream, an initial representation of H1 has been investigated in which the ice loss is assumed to proceed up the strait to Southampton Island over a period constrained by observations. The tidal energy and dissipation associated with the dominant M2 semidiurnal tide were found to be extremely high relative to their modern strengths prior to H1 but dropped sharply after the instability occurred. A globally averaged (eustatic) sea level rise of approximately 1 m associated directly with this simple model is inferred. The high‐amplitude tides at the Atlantic outlet of the Hudson Strait are further demonstrated to track inland with the retreating ice up the strait as the instability of the ice stream migrates inland at a moderate speed consistent with estimates of the inferred instability event duration.

Plain Language Summary
Heinrich events, which occurred during the most recent ice age, involved large amounts of ice being released from the Hudson Strait into the North Atlantic over a short period of time. In this paper, a numerical model of the tides is used to investigate the relationship between tidal forcing and Heinrich events. In the model of Heinrich event 1 employed, we find that the energy of the M2 tidal constituent drops after H1, that high‐amplitude tides track inland with the retreating ice stream, and that the disintegration of this ice stream produces approximately 1 m of sea level rise. This indicates that the tides may serve as both a trigger and forcing for Heinrich events.

Extract: "Nevertheless, the fact that the Heinrich event instability is recurrent under ice age conditions is strongly suggestive of a system that is continually revisiting a point of instability and therefore is an example of the self‐organized criticality phenomenon."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Hefaistos

  • Grease ice
  • Posts: 719
    • View Profile
  • Liked: 74
  • Likes Given: 471
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #3679 on: August 22, 2020, 11:18:51 AM »
The linked (open access) reference examines the CMIP6 model results in order to try to establish constraints on values of TCR.  However, the associated attached image shows that several CMIP6 models (such as CESM2_WACCM) project both relatively low values of TCR and relatively high values of ECS; which raises the prospect that with continued radiative forcing climate sensitivity could accelerate nonlinearly in the coming decades:

Nijsse, F. J. M. M., Cox, P. M., and Williamson, M. S.: An emergent constraint on Transient Climate Response from simulated historical warming in CMIP6 models, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2019-86, in review, 2020.

https://www.earth-syst-dynam-discuss.net/esd-2019-86/

Abstract. The transient climate response (TCR) is the metric of temperature sensitivity that is most relevant to warming in the next few decades, and contributes the biggest uncertainty to estimates of the carbon budgets consistent with the Paris targets (Arora et al., 2019). In the IPCC 5th Assessment Report (AR5), the stated likely range of TCR was given as 1.0 to 2.5 K, with a central estimate which was broadly consistent with the ensemble mean of the CMIP5 Earth System Models (ESMs) available at the time (1.8 ± 0.4 K). Many of the latest CMIP6 ESMs have larger climate sensitivities, with 6 of 23 models having TCR values above 2.5 K, and an ensemble mean TCR of 2.1 ± 0.4 K. On the face of it, these latest ESM results suggest that the IPCC likely range of TCR may need revising upwards, which would cast further doubt on the feasibility of the Paris targets. Here we show that rather than increasing the uncertainty in climate sensitivity, the CMIP6 models help to further constrain the likely range of TCR to 1.5–2.2 K, with a central estimate of 1.82 K. We reach this conclusion through an emergent constraint approach which relates the value of TCR to the global warming from 1970 onwards. We confirm a consistent emergent constraint on TCR when we apply the same method to CMIP5 models (Jiménez-de-la Cuesta and Mauritsen, 2019). Our emergent constraint on TCR benefits from both the large range of TCR values across the CMIP6 models, and also from the extension of the historical simulations into a period when the uncertain changes in aerosol forcing have had a far less significant impact on the trend in global warming.

Note that this is good news.  TCR is what we're dealing with in the next few decades as we transition from fossil fuels to carbon free energy sources.  ECS is what happens over the centuries as the climate comes into equilibrium from the forcings.

And it shows that even with the CMIP6 models coming up with higher ECS, the results from those models for TCR are consistent with the CMIP5 models used for AR5.  It looks like consensus science got TCR right.

The paper has now been published, 17.08.2020, after peer review.
https://esd.copernicus.org/articles/11/737/2020/

Nic Lewis thinks it shouldn't have been published, in this critical review:

"... there is a fatal problem with the regression method used to relate TCR with warming...
My key point is that an analysis method that results in a physically reasonable estimated relationship between the variables being studied should be used. An estimated relationship that implies zero warming with a positive TCR, and significant cooling with a zero TCR, is unphysical. Therefore, the results of the Nijsse et al. paper are unreliable and should be discounted."

https://www.nicholaslewis.org/emergent-constraints-on-tcr-and-ecs-from-historical-warming-in-cmip5-and-cmip6-models/

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3680 on: August 23, 2020, 04:06:46 PM »
The linked reference associates Heinrich events and Dansgaard-Oeschger cycles (or events) can be related to MICI mechanisms:

Bassis, J., Petersen, S. & Mac Cathles, L. Heinrich events triggered by ocean forcing and modulated by isostatic adjustment. Nature 542, 332–334 (2017). https://doi.org/10.1038/nature21069

https://www.nature.com/articles/nature21069?WT.feed_name=subjects_geodynamics

...

The linked reference build on earlier research on Dansgaard–Oeschger (D-O) cycles [including that from Bassis et al. (2017) for Henrich events] to propose a conceptual model emphasizing ocean circulation (AMOC), ice shelf and sea ice and bipolar seesaw interactions to better explain D-O cycles.  Furthermore, many of the conceptual ice-ocean interactions are relevant to the current instability of the WAIS (especially if the AMOC is abruptly modified by a reversal of the Beaufort Gyre in coming decades).

Niklas Boers et al. (November 20, 2018), "Ocean circulation, ice shelf, and sea ice interactions explain Dansgaard–Oeschger cycles", PNAS, 115, (47), E11005-E11014; https://doi.org/10.1073/pnas.1802573115

https://www.pnas.org/content/115/47/E11005

Significance
Paleoclimatic proxy records from Greenland ice cores show that the last glacial interval was punctuated by abrupt climatic transitions called Dansgaard–Oeschger (DO) events. These events are characterized by temperature increases over Greenland of up to 15°C within a few decades. The cause of these transitions and their out-of-phase relationship with corresponding records from Antarctica remains unclear. Based on earlier hypotheses, we propose a model focusing on interactions between ice shelves, sea ice, and ocean currents to explain DO events in Greenland and their Antarctic counterparts. Our model reproduces the main features of the observations. Our study provides a potential explanation of DO events and could help assess more accurately the risk of abrupt climatic transitions in the future.

Abstract
The last glacial interval experienced abrupt climatic changes called Dansgaard–Oeschger (DO) events. These events manifest themselves as rapid increases followed by slow decreases of oxygen isotope ratios in Greenland ice core records. Despite promising advances, a comprehensive theory of the DO cycles, with their repeated ups and downs of isotope ratios, is still lacking. Here, based on earlier hypotheses, we introduce a dynamical model that explains the DO variability by rapid retreat and slow regrowth of thick ice shelves and thin sea ice in conjunction with changing subsurface water temperatures due to insulation by the ice cover. Our model successfully reproduces observed features of the records, such as the sawtooth shape of the DO cycles, waiting times between DO events across the last glacial, and the shifted antiphase relationship between Greenland and Antarctic ice cores. Our results show that these features can be obtained via internal feedbacks alone. Warming subsurface waters could have also contributed to the triggering of Heinrich events. Our model thus offers a unified framework for explaining major features of multimillennial climate variability during glacial intervals.

Extract: "Corresponding δ18O time series obtained from Antarctic ice cores show an antiphase relationship with the temporal evolution in Greenland, with gradual increases during Greenland stadials and gradual cooling during Greenland interstadials (10–12) (compare with Fig. 1). A recent study based on a high-resolution Antarctic ice core estimates a delay of roughly 200 y between DO events in Greenland and the onset of cooling in Antarctica as well as between the return to stadial conditions in Greenland and the onset of warming in Antarctica. From the sign and magnitude of this delay, an oceanic north-to-south transmission of the climatic signal has been inferred (12).

Since the DO events are outstanding examples of abrupt and dramatic climate transitions in the past, a better understanding of the underlying mechanisms is urgently needed to better assess the risk of abrupt climatic transitions in the future.

Variations in marginal ice sheets, ice shelves, and sea ice cover near Greenland and other North Atlantic basin coasts, possibly in concert with AMOC changes, have also been proposed to explain the observed DO cycles (23, 25–29). Model results suggest that Nordic Sea sea ice retreat can increase winter temperatures by 10°10° C (30). Furthermore, it has been shown that freshwater pulses induced by iceberg discharges can trigger DO-type oscillations via coherence resonance (31). The latter study also provides a possible explanation for the suggested relationship between DO events and Heinrich events (32–34), which are characterized by massive iceberg discharges into the Labrador Sea. These discharges are evident as pronounced bands of ice-rafted debris in marine sediment cores (34). The Heinrich events themselves might have been triggered by warming subsurface waters in the northern North Atlantic during stadial conditions (35–38). Heinrich-type iceberg calving occurs during the cooler stadials, possibly acting as a feedback stabilizing the stadial conditions (39, 40). It should be noted here that—in addition to the Heinrich events, during which icebergs were mainly discharged into the Labrador Sea—there is empirical evidence for substantial iceberg discharges at several other locations around the northern North Atlantic (41) and in particular, into the Denmark Straight and Icelandic Sea (23, 42).

To our knowledge, studies focusing on sea ice or ice shelf variability to explain the DO events do not account for the antiphase coupling between Greenland and Antarctic temperatures (compare with Fig. 1 and ref. 12), and they do not account for the fact that, even in high northern latitudes, subsurface water temperatures are in phase with the temperature evolution observed in Antarctica (49). A possible explanation for these couplings is that reductions in North Atlantic subsurface water temperatures at the DO onset lead to a switch of the AMOC from its weak mode to its strong mode. Recent observational evidence of an approximately 200-y lag between Greenland and Antarctic temperatures, suggesting an oceanic north-to-south propagation of the climatic signal (12), supports this hypothesis. Note that, in such a setting, changes in AMOC strength would not be the cause but rather, a consequence of the DO events.

In this paper, we test the hypothesis that Greenland ice shelves and sea ice interact with the AMOC to produce the observed DO cycles and the shifted antiphase relationship between the two hemispheres.

A key ingredient of our model is that heat transported northward by the AMOC accumulates below ice shelves and sea ice and eventually, removes the ice cover. So far, we only suggested this mechanism for a hypothesized Greenland ice shelf to trigger DO events; it could, however, apply—at least during some Greenland stadials—also for the Laurentide and Fennoscandian ice sheets or the ice shelves attached to either one of them. The ice sheets themselves could have been destabilized directly (60) or by the removal of the attached ice shelves. The resulting massive iceberg discharges would then cause the pronounced bands of ice-rafted debris in marine sediments that mark the Heinrich events (32–36, 38, 41).

The model proposed herein reproduces the key features associated with DO cycles during the last glacial interval, including the sawtooth shape of the DO oscillations in Greenland—with its two-step cooling from interstadials to stadials—as well as the correct waiting times between the DO events across the last glacial and the shifted antiphase relationship with Antarctica. No external forcing was included in our model to trigger the DO events, implying that these oscillations can be produced by internal feedbacks alone.

38. Bassis JN, Petersen SV, Mac Cathles L (2017) Heinrich events triggered by ocean forcing and modulated by isostatic adjustment. Nature 542:332–334.

Caption for the first image: "Fig. 1. Variability of the last glacial interval as expressed by oxygen isotope ratios (δ18O). Blue indicates Greenland δ18O data obtained from the NGRIP (3) at a regular sampling rate of 20 y (13). Orange indicates Antarctic δ18O data from the WAIS ice core (12). As in ref. 12, the layer-counted NGRIP chronology GICC05 (14, 15) is rescaled by a factor of 1.0063, because the layer-counted WAIS divide deep ice core chronology (WD2014) (16), on which the WAIS δ18Oδ18O record is shown, is synchronized to this rescaled chronology. The δ18O values are commonly interpreted as a proxy for atmospheric temperatures at the location of the ice core, with higher values indicating warmer temperatures. The training period for our model is the interval from 59 to 23 ky b2k, which roughly corresponds to Marine Isotope Stage 3 (MIS3). DO events are indicated by vertical magenta lines, Heinrich stadials are marked by grey shading, and MISs are indicated at the top of the figure. The thin vertical dashed lines indicate time steps in intervals of 20 ky. Inset shows the geographical locations of the NGRIP and WAIS sites and a sketch of the oceanic circulation, with warmer surface flow in red and colder bottom flow in blue."

Caption for the second image: "Fig. 2. Schematic diagram of typical stadial and interstadial conditions during the last glacial interval together with the relevant observables included in the proposed model: δ18O in Greenland cores (IGIG), atmospheric temperature in Greenland (TGTG), subsurface water temperatures in the northern North Atlantic (TNAWTNAW), extent of ice cover close to Greenland (C), AMOC strength (ψ), and δ18O in Antarctic cores (IAIA); details are in the text. The blue arrows indicate the distinct atmospheric paths of δ18O from the evaporative source in the Atlantic Ocean to the ice core site in northern Greenland. Small and large fonts correspond to low and high values, respectively, of the observables. Inset shows the feedback mechanisms involved; here, solid arrows indicate a positive or enhancing influence, while dashed arrows indicate a negative or damping influence."

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #3681 on: August 23, 2020, 06:47:29 PM »
The linked reference address how the collapse of the WAIS can alter oceanic and atmospheric patterns, leading to Super Interglacial conditions:

Flavio Justino, Douglas Lindemann, Fred Kucharski, Aaron Wilson, David Bromwich, and Frode Stordal (2017), "Oceanic response to changes in the WAIS and astronomical forcing during the MIS31 superinterglacial", Clim. Past, 13, 1081–1095, https://doi.org/10.5194/cp-13-1081-2017

https://www.clim-past.net/13/1081/2017/cp-13-1081-2017.pdf

...

As it is possible that we are collectively heading towards a Super-Interglacial period, beginning in coming decades, I provide the linked collection of references related to Super-Interglacial periods largely based on paleo-findings from Lake El'gygytgyn.

In this regard, I note that MIS 11c was a Super-Interglacial period while MIS 5e was not, and that Wet et al. (2016) states: "Based on brGDGT temperatures from Lake El'gygytgyn (this study and unpublished results), warming in the western Arctic during MIS 31 was matched only by MIS 11 during the Pleistocene."

Also, Wennrich et al. (September 2016) states: "Periods of exceptional warming in the Pleistocene record of Lake El'gygytgyn with dense boreal forests around and peaks of primary production in the lake are assigned to so-called “super-interglacial” periods. The occurrence of these super-interglacials well corresponds to collapses of the West Antarctic Ice Sheet (WAIS) recorded in ice-free periods in the ANDRILL core, which suggests strong intrahemispheric teleconnections presumably driven by changes in the thermocline ocean circulation."

Also, Brigham-Grette et al. (2018) states: "While WAIS may have been gone in MIS 5e, this was not a super interglacial by Arctic standards. This suggests thresholds of sensitivity in the earth system."

Also, Brigham-Grette et al. (2019) states: "When the Bering Strait is closed, models suggest more ocean heat transported into the Arctic, improving the fit between extremely warm Pliocene marine and terrestrial records. Yet the depth of Bering Strait over time is unknown due to glacial isostatic adjustments, dynamic topography and regional tectonics, the last being generally neglected by the paleoclimate community."

Gregory A.de Wet, Isla S. Castañeda, Robert M. DeConto and Julie Brigham-Grette (15 February 2016), "A high-resolution mid-Pleistocene temperature record from Arctic Lake El'gygytgyn: a 50 kyr super interglacial from MIS 33 to MIS 31?", Earth and Planetary Science Letters, Volume 436,  Pages 56-63, https://doi.org/10.1016/j.epsl.2015.12.021

https://www.sciencedirect.com/science/article/abs/pii/S0012821X15007840

Abstract
Previous periods of extreme warmth in Earth's history are of great interest in light of current and predicted anthropogenic warming. Numerous so called “super interglacial” intervals, with summer temperatures significantly warmer than today, have been identified in the 3.6 million year (Ma) sediment record from Lake El'gygytgyn, northeast Russia. To date, however, a high-resolution paleotemperature reconstruction from any of these super interglacials is lacking. Here we present a paleotemperature reconstruction based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) from Marine Isotope Stages (MIS) 35 to MIS 29, including super interglacial MIS 31. To investigate this period in detail, samples were analyzed with an unprecedented average sample resolution of 500 yrs from MIS 33 to MIS 30. Our results suggest the entire period currently defined as MIS 33–31 (∼1114–1062 kyr BP) was characterized by generally warm and highly variable conditions at the lake, at times out of phase with Northern Hemisphere summer insolation, and that cold “glacial” conditions during MIS 32 lasted only a few thousand years. Close similarities are seen with coeval records from high southern latitudes, supporting the suggestion that the interval from MIS 33 to MIS 31 was an exceptionally long interglacial (Teitler et al., 2015). Based on brGDGT temperatures from Lake El'gygytgyn (this study and unpublished results), warming in the western Arctic during MIS 31 was matched only by MIS 11 during the Pleistocene.

&

Volker Wennrich et al. (September 2016), "Impact processes, permafrost dynamics, and climate and environmental variability in the terrestrial Arctic as inferred from the unique 3.6 Myr record of Lake El'gygytgyn, Far East Russia – A review", Quaternary Science Reviews, Volume 147, 1, Pages 221-244, https://doi.org/10.1016/j.quascirev.2016.03.019

https://www.sciencedirect.com/science/article/abs/pii/S0277379116300877

Abstract
Lake El'gygytgyn in Far East Russia is a 3.6 Myr old impact crater lake. Located in an area that has never been affected by Cenozoic glaciations nor desiccation, the unique sediment record of the lake represents the longest continuous sediment archive of the terrestrial Arctic. The surrounding crater is the only impact structure on Earth developed in mostly acid volcanic rocks. Recent studies on the impactite, permafrost, and sediment sequences recovered within the framework of the ICDP “El'gygytgyn Drilling Project” and multiple pre-site surveys yielded new insight into the bedrock origin and cratering processes as well as permafrost dynamics and the climate and environmental history of the terrestrial Arctic back to the mid-Pliocene.
Results from the impact rock section recovered during the deep drilling clearly confirm the impact genesis of the El'gygytgyn crater, but indicate an only very reduced fallback impactite sequence without larger coherent melt bodies. Isotope and element data of impact melt samples indicate a F-type asteroid of mixed composition or an ordinary chondrite as the likely impactor. The impact event caused a long-lasting hydrothermal activity in the crater that is assumed to have persisted for c. 300 kyr.

Geochemical and microbial analyses of the permafrost core indicate a subaquatic formation of the lower part during lake-level highstand, but a subaerial genesis of the upper part after a lake-level drop after the Allerød. The isotope signal and ion compositions of ground ice is overprinted by several thaw-freeze cycles due to variations in the talik underneath the lake. Modeling results suggest a modern permafrost thickness in the crater of c. 340 m, and further confirm a pervasive character of the talik below Lake El'gygytgyn.

The lake sediment sequences shed new leight into the Pliocene and Pleistocene climate and environmental evolution of the Arctic. During the mid-Pliocene, significantly warmer and wetter climatic conditions in western Beringia than today enabled dense boreal forests to grow around Lake El'gygytgyn and, in combination with a higher nutrient flux into the lake, promoted primary production. The exceptional warmth during the mid-Pliocene is in accordance with other marine and terrestrial records from the Arctic and indicates a period of enhanced “Arctic amplification”. The favourable conditions during the mid-Pliocene were repeatedly interrupted by climate deteriorations, e.g., during Marine Isotope Stage (MIS) M2, when pollen data and sediment proxies indicate a major cooling and the onset of local permafrost around the lake.

A gradual vegetation change after c. 3.0 Ma points to the onset of a long-term cooling trend during the Late Pliocene that culminated in major temperature drops, first during MIS G6, and later during MIS 104. These cold events coincide with the onset of an intensified Northern Hemisphere (NH) glaciation and the largest extent of the Cordilleran Ice Sheet, respectively.
After the Pliocene/Pleistocene transition, local vegetation and primary production in Lake El'gygtygyn experienced a major change from relatively uniform conditions to a high-amplitude glacial-to-interglacial cyclicity that fluctuated on a dominant 41 kyr obliquity band, but changed to a 100 kyr eccentricity dominance during the Middle Pleistocene transition (MPT) at c. 1.2–0.6 Ma. Periods of exceptional warming in the Pleistocene record of Lake El'gygytgyn with dense boreal forests around and peaks of primary production in the lake are assigned to so-called “super-interglacial” periods. The occurrence of these super-interglacials well corresponds to collapses of the West Antarctic Ice Sheet (WAIS) recorded in ice-free periods in the ANDRILL core, which suggests strong intrahemispheric teleconnections presumably driven by changes in the thermocline ocean circulation.

&

Title: "PP22A-04: Interglacial Intensity with Orbital Pre-conditioning Links Polar Ice Sheet Sensitivity to Warming (Invited)" by Julie Brigham-Grette, Rajarshi Roychowdhury, Robert M Deconto, Isla S. Castañeda and Helen Habicht (2018)

https://agu.confex.com/agu/fm18/meetingapp.cgi/Paper/354878

Abstract: "Paleoclimate records of climate change from northeast Arctic Russia (Lake El’gygytgyn) and Antarctica over the past 3-4 Million years provide a new opportunity for understanding the sensitivity of the polar regions to forcings involving natural greenhouse gas variability, changing orbital configurations and associated feedbacks. While geography and transient atmospheric CO2 in excess of preindustrial levels can explain most of the Pliocene warming, the occurrence of Arctic super interglacials without clear pacing documented over the past 2.78 Myrs requires additional explanation. Not all interglacials are alike and the strength of the interglacial might be function of the proxy used for its identification. We hypothesize that numerous super interglacials in the Arctic correspond with extremes in insolation leading to the demise of the WAIS. During MIS 11c, 31, 49, 55, 77, 87, 91, and 93 Milankovitch forcing coinciding with extreme lows in eccentricity and high obliquity likely preconditioned the Earth system to synchronize summer melt intensity and duration to produce bipolar warming. The challenge has been to understand how these high latitude sites are linked with changes in ocean circulation, gateway changes, and heat transport. This preconditioned warming likely led to the demise of the WAIS in the Southern Hemisphere and super interglacials in the Arctic Northern Hemisphere. Diatomite layers in the ANDRILL AND-1B record coincide reasonably well super interglacials (Melles et al, 2012) but unconformities in the AND-1B cores prevent direct correlation. While WAIS may have been gone in MIS 5e, this was not a super interglacial by Arctic standards. This suggests thresholds of sensitivity in the earth system."

&

Title: “Beringia as the Arctic Pacific Gateway – Interglacial intensity since the Pliocene and Why its Sea Level History just got Thorny.” by Julie Brigham-Grette and Beth Caissie (2019)

https://sites.uw.edu/amqua50/julie-brigham-grette/

Abstract: The paleoclimate history of Beringia, the largest contiguous land area not covered by continental scale glaciation, provides remarkable archives of the late Cenozoic history of the Arctic Borderlands. Lake El’gygytgyn in western Beringia contains the most continuous record of glacial/interglacial change of the past 3.6 Ma, demonstrating unprecedented evidence for super interglacials and the evolving pace of glacial/interglacial change. Similarly, the International Ocean Discovery Program’s 5 Myr long records in the Bering Sea document the submergence and emergence history of the Pacific Arctic marine gateway revealing how relatively fresher North Pacific waters influenced Atlantic Meridional Overturning Circulation and changes in the production of North Pacific intermediate water production. When the Bering Strait is closed, models suggest more ocean heat transported into the Arctic, improving the fit between extremely warm Pliocene marine and terrestrial records. Yet the depth of Bering Strait over time is unknown due to glacial isostatic adjustments, dynamic topography and regional tectonics, the last being generally neglected by the paleoclimate community. Indeed, paleoseismic evidence shows the Bering Sea has been rotating clockwise for the past 6 Myrs with the active Kobuk fault cutting directly across Bering Strait. Integrating both the land and sea records is now possible.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3682 on: August 24, 2020, 03:06:57 AM »
As interstadial events are likely tied to marine ice-cliff failure mechanisms, the linked reference will hopefully make it easier to calibrate climate models to better understand the risks of abrupt climate change.

Ellen C. Corrick et al. (21 Aug 2020). "Synchronous timing of abrupt climate changes during the last glacial period", Science, Vol. 369, Issue 6506, pp. 963-969, DOI: 10.1126/science.aay5538

https://science.sciencemag.org/content/369/6506/963

All together then
Many geographically dispersed records from across the globe reveal the occurrence of abrupt climate changes, called interstadial events, during the last glacial period. These events appear to have happened at the same time, but the difficulty of determining absolute dates in many of the records have made that proposition difficult to prove. Corrick et al. present results from 63 precisely dated speleothems that confirm the synchrony of those interstadial events. Their results also provide a tool with which to validate model simulations of abrupt climate change and calibrate other time series such as ice-core chronologies.

Science, this issue p. 963

Abstract
Abrupt climate changes during the last glacial period have been detected in a global array of palaeoclimate records, but our understanding of their absolute timing and regional synchrony is incomplete. Our compilation of 63 published, independently dated speleothem records shows that abrupt warmings in Greenland were associated with synchronous climate changes across the Asian Monsoon, South American Monsoon, and European-Mediterranean regions that occurred within decades. Together with the demonstration of bipolar synchrony in atmospheric response, this provides independent evidence of synchronous high-latitude–to-tropical coupling of climate changes during these abrupt warmings. Our results provide a globally coherent framework with which to validate model simulations of abrupt climate change and to constrain ice-core chronologies.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

sidd

  • First-year ice
  • Posts: 5685
    • View Profile
  • Liked: 788
  • Likes Given: 0
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3683 on: August 24, 2020, 07:06:03 AM »
I commented about that paper in another thread, it is a really strong combination of NGRIP and speleothems. Unfortunately the paper is not open access, but perhaps it will show up on scihub or researchgade or something. The supplementaries are open, and the figures are very well worth looking at.

sidd

vox_mundi

  • Young ice
  • Posts: 4107
    • View Profile
  • Liked: 2399
  • Likes Given: 318
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3684 on: August 24, 2020, 03:34:06 PM »
Japanese Expedition Identifies East Antarctic Melting Hotspot
https://phys.org/news/2020-08-japanese-east-antarctic-hotspot.html

Ice is melting at a surprisingly fast rate underneath Shirase Glacier Tongue in East Antarctica due to the continuing influx of warm seawater into the Lützow-Holm Bay.



... "Our data suggests that the ice directly beneath the Shirase Glacier Tongue is melting at a rate of seven to 16 meters per year," says Assistant Professor Daisuke Hirano of Hokkaido University's Institute of Low Temperature Science. "This is equal to or perhaps even surpasses the melting rate underneath the Totten Ice Shelf, which was thought to be experiencing the highest melting rate in East Antarctica, at a rate of 10 to 11 meters per year."

... The data suggests the melting is occurring as a result of deep, warm water flowing inward, toward the base of the Shirase Glacier Tongue. The warm water moves along a deep underwater ocean trough and then flows upward along the tongue's base, warming and melting the ice. The warm waters carrying the melted ice then flow outwards, mixing with the glacial meltwater.

The team found this melting occurs year-round, but is affected by easterly, winds alongshore that vary seasonally. When the winds diminish in the summer, the influx of the deep warm water increases, speeding up the melting rate.



Daisuke Hirano et al., Strong ice-ocean interaction beneath Shirase Glacier Tongue in East Antarctica. Nature Communications (2020)
https://www.nature.com/articles/s41467-020-17527-4
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― Leonardo da Vinci

Insensible before the wave so soon released by callous fate. Affected most, they understand the least, and understanding, when it comes, invariably arrives too late

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3685 on: August 24, 2020, 05:54:15 PM »
I provide again the following linked reference that considers the collapse of the Hudson Strait Ice Stream (within the paleo Laurentide Ice Sheet see the first image), as a rough physical model of the potential collapse of the 'ice plug' in the Thwaites Gateway (i.e. before the grounding line reaches the retrograde bedslope).  The second image shows that immediately after the loss of the ice shelf for the Hudson Strait Ice Steam [see also third image from Alvarez-Solas et al. (2012)], the ice loss surged (even though the water depths are comparable to those in the Thwaites Gateway).  Furthermore, I remind readers that the Hudson Strait Ice Stream repeated retreats could only be due to MICI mechanisms as they produced extensive ice-rafted debris fields and that these retreats occurred during glacial periods when hydrofracturing could not have occurred.  Finally, I note that paleo MICI events Antarctica have pre-conditioned the beds of key marine glaciers (like Thwaites, PIG and Totten), which increases their probability of collapse in current times as compared to paleo times.


Ziemen, F. A., Kapsch, M.-L., Klockmann, M., and Mikolajewicz, U.: Heinrich events show two-stage climate response in transient glacial simulations, Clim. Past, 15, 153-168, https://doi.org/10.5194/cp-15-153-2019, 2019.

https://www.clim-past.net/15/153/2019/

Abstract. Heinrich events are among the dominant modes of glacial climate variability. During these events, massive iceberg armadas were released by the Laurentide Ice Sheet and sailed across the Atlantic where they melted and released freshwater, as well as detritus, that formed characteristic layers on the seafloor. Heinrich events are known for cold climates in the North Atlantic region and global climate changes. We study these events in a fully coupled complex ice sheet–climate model with synchronous coupling between ice sheets and oceans. The ice discharges occur as an internal variability of the model with a recurrence period of 5kyr, an event duration of 1–1.5kyr, and a peak discharge rate of about 50mSv, roughly consistent with reconstructions. The climate response shows a two-stage behavior, with freshwater release effects dominating the surge phase and ice sheet elevation effects dominating the post-surge phase. As a direct response to the freshwater discharge during the surge phase, deepwater formation in the North Atlantic decreases and the North Atlantic deepwater cell weakens by 3.5Sv. With the reduced oceanic heat transport, the surface temperatures across the North Atlantic decrease, and the associated reduction in evaporation causes a drying in Europe. The ice discharge lowers the surface elevation in the Hudson Bay area and thus leads to increased precipitation and accelerated ice sheet regrowth in the post-surge phase. Furthermore, the jet stream widens to the north, which contributes to a weakening of the subpolar gyre and a continued cooling over Europe even after the ice discharge. This two-stage behavior can explain previously contradicting model results and understandings of Heinrich events.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3686 on: August 24, 2020, 06:52:51 PM »
Climate change is so complex that the Bank of International Settlement (BIS) has created the term of 'Green Swan' that contains considerations beyond traditional financial 'Black Swan' events, including the risks that a cascade of tipping points could well produce future conditions that have not been evaluated by consensus climate science:

Title: "Green swans: Why climate change is unlike any other financial risk"

https://www.intheblack.com/articles/2020/08/17/why-climate-change-unlike-other-financial-risk

Extract: "Perhaps the most noteworthy feature of black swan events, and that which now influences the policy thinking of such groups as the Bank of International Settlements (BIS), is their probabilistic characteristics. Unlike normal distributions, these events typically are non-linear in nature, heavily skewed with fat-tailed probability distributions.

This makes redundant, backward-looking approaches to understanding risk given their occurrence not being reflected in past data coupled with the possibility of extreme values.

Both transition and physical climate-related risks demonstrate features of black swan events, hence the BIS’s adaptation of the phrase “green swan”.

The BIS draws out three additional complexities which make even more profound the challenges in guiding their advice to central banks:

First, the scientific consensus from the Intergovernmental Panel on Climate Change (2018) points to a growing gap between current temperature trends and emissions reductions targets, leading to somewhere between 3ºC and 4ºC of warming.

This is illustrative of ongoing uncertainty about the strength and effectiveness of public policy and the timing of emissions reduction trajectories.

Secondly, climate catastrophes are potentially more serious than systemic financial crises, as they pose an existential threat to economies and humanity, with potential for very deep cuts in global GDP.

Thirdly, complexity is of a much higher order with potential for complex chain reactions and cascading effects across both physical and transition dimensions generating further unpredictability in environmental, geopolitical, social and economic dynamics."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Tor Bejnar

  • Young ice
  • Posts: 3637
    • View Profile
  • Liked: 633
  • Likes Given: 407
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3687 on: August 24, 2020, 07:49:32 PM »
Quote
... and that these retreats occurred during glacial periods when hydrofracturing could not have occurred.
(from 2 posts up)
I laughed out loud, Abrupt.  (just so you know someone's reading your posts, at least the parts you write)
Arctic ice is healthy for children and other living things.

Lennart van der Linde

  • Grease ice
  • Posts: 780
    • View Profile
  • Liked: 83
  • Likes Given: 6
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3688 on: August 24, 2020, 08:46:05 PM »
Climate change is so complex that the Bank of International Settlement (BIS) has created the term of 'Green Swan' that contains considerations beyond traditional financial 'Black Swan' events, including the risks that a cascade of tipping points could well produce future conditions that have not been evaluated by consensus climate science:

Title: "Green swans: Why climate change is unlike any other financial risk"

https://www.intheblack.com/articles/2020/08/17/why-climate-change-unlike-other-financial-risk

Thanks for this pointer!

gerontocrat

  • First-year ice
  • Posts: 9328
    • View Profile
  • Liked: 3727
  • Likes Given: 28
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3689 on: August 24, 2020, 10:19:57 PM »
Climate change is so complex that the Bank of International Settlement (BIS) has created the term of 'Green Swan' that contains considerations beyond traditional financial 'Black Swan' events, including the risks that a cascade of tipping points could well produce future conditions that have not been evaluated by consensus climate science:

Title: "Green swans: Why climate change is unlike any other financial risk"

https://www.intheblack.com/articles/2020/08/17/why-climate-change-unlike-other-financial-risk

climate catastrophes are potentially more serious than systemic financial crises, as they pose an existential threat to economies and humanity, with potential for very deep cuts in global GDP.

The BIS is "The Central Bankers' Bank" and puts reports into the Public Domain rarely. I note from the article that they do not seem to have done so this time. The article is by the CPA Australia.

The BIS also has a track record of being right - but so much in advance they are ignored by Governments. They first reported in 2003 that the financial trends at the time would inevitably lead to the financial crisis of 2008-2010. Governments ignored them.

I wonder if they will be inclined to put something into the Public Domain to add some pressure to the 2021 IPCC meeting?

So given that time lag, perhaps the proverbial will hit the proverbial towards the end of the 2020's ?
« Last Edit: August 24, 2020, 10:30:11 PM by gerontocrat »
"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
"Damn, I wanted to see what happened next" (Epitaph)

Lennart van der Linde

  • Grease ice
  • Posts: 780
    • View Profile
  • Liked: 83
  • Likes Given: 6
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3690 on: August 24, 2020, 10:42:20 PM »
I note from the article that they do not seem to have done so this time. The article is by the CPA Australia...

I wonder if they will be inclined to put something into the Public Domain to add some pressure to the 2021 IPCC meeting?

They did put it in the public domain in January 2020, with the express purpose of putting pressure on international society:
https://www.bis.org/publ/othp31.htm

Also see a follow-up from May 2020, discussing the climate and Corona-crises:
https://www.bis.org/speeches/sp200514.htm

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3691 on: August 25, 2020, 04:16:08 PM »
Quote
... and that these retreats occurred during glacial periods when hydrofracturing could not have occurred.
(from 2 posts up)
I laughed out loud, Abrupt.  (just so you know someone's reading your posts, at least the parts you write)

While I appreciate a good sense of humor, I am concerned that some readers may become so distracted by how funny an elephant's tail can look from some angles (see the first image) and forget the tail-risk that that tail might be attached to a raging bull elephant.  For instance, the second image shows that during the last glacial period the is a clear correlation between NH and SH MICI events that clearly indicates an active bipolar seesaw mechanism was in play then and I note that during this period there were a large number of marine glaciers resting on the Antarctic continental shelf (including in Pine Island Bay) that were participating in such a bipolar seesaw mechanism.

Next, the third image shows that in their MICI model Pollard et al. (2015) finds that hydrofracturing can greatly accelerate the collapse of Antarctic ice shelves and thus can accelerate the rate of MICI collapse of marine ice sheets.  However, I note that the Thwaites Ice Tongue is already so degraded that hydrofracturing is not needed to trigger ice cliff failure mechanisms in the Thwaites Gateway as by circa 2035 the currently grounded icebergs at the base of the Thwaites Ice Tongue could readily float-away during a Super El Nino event, exposing an ice cliff face that could trigger an MICI type of failure of the Byrd Subglacial Basin.

Title: Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure" by Pollard et al (2015)

https://www.sciencedirect.com/science/article/pii/S0012821X14007961

Caption for the third image: "Fig. 4. Global mean equivalent sea level rise in warm-climate simulations. Time series of global mean sea level rise above modern are shown, implied by reduced Antarctic ice volumes. The calculation takes into account the lesser effect of melting ice that is originally grounded below sea level. Cyan: with neither cliff failure nor melt-driven hydrofracturing active. Blue: with cliff failure active. Green: with melt-driven hydrofracturing active. Red: with both these mechanisms active. Geographic ice distributions for the latter run are shown in Fig. 3, and for the other runs in Fig. 5."

Edit: For those who prefer to consider paleo-evidence for an MICI collapse of the WAIS during a recent interglacial period, I repost the following:

The video embedded in the linked article confirms that research in both Tahiti and Barbados confirms that at periods in the past sea level has increased at rates of 10-ft per century; which if replicated in coming decades would have major impacts on global socio-economic systems:

Title: "How High Can Seas Rise? On a Tropical Isle, the Answers Are Not Always Obvious."

https://www.ldeo.columbia.edu/news-events/how-high-can-seas-rise-tropical-isle-answers-are-not-always-obvious

Extract: "A 2009 study done in Barbados by other researchers suggests that 121,000 years ago, seas rose as much as 9 feet in just a century—perhaps due to a sudden collapse of the Western Antarctic Ice Sheet. If it could happen then, it could happen now, said Raymo. Using the newly exacting methods, she wanted to see if it really was so.

Barbados is a good place to start, though, she said, not only because of its fossil corals, but because it is close to the equator and relatively isolated from most effects except water level itself. “We like to call Barbados the dipstick of sea level,” she said."
« Last Edit: August 25, 2020, 04:26:03 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3692 on: August 25, 2020, 05:48:43 PM »
While only E3SMv1 output will be considered in AR6, the linked article (& the first image) considers some of the efforts to improvement the modeling of Atmospheric Physics for first E3SMv2 circa 2021 (see the second image) and then E3SMv3.  For what it is worth I note that improving the modeling of Deep Convection in atmosphere is particularly important in the Tropical Pacific as the increased production of high-altitude clouds in this region could increase projections of climate sensitivity particularly if/when the MOC continues to slow.  Also, I note that a lot of the relatively strong aerosol forcing (as compared to CMIP5 estimates) estimated by E3SMv1 was associated with the emissions pattern resulting from use of SSP scenarios rather than concentrations from use of RCP scenarios in CMIP5; and thus this aerosol pattern effect will not change even if E3SMv2 reduces its Aerosol Indirect Effect (AIE) routines.

Title: "NGD Atmospheric Physics"

https://e3sm.org/about/organization/ngd-sub-projects/ngd-atmospheric-physics/

Extract: "One of E3SM’s Phase Two Next Generation Development (NGD) efforts is to continue improving the current model’s representation of atmospheric physics and enhance the model’s capability to address uncertainty in predicting future changes enabling scientists to address questions across the Water cycle, Biogeochemistry (BGC), and Cryosphere campaigns. The NGD-Atmospheric Physics project, led by Shaocheng Xie of Lawrence Livermore National Laboratory (LLNL), consists of more than 30 scientists from four DOE labs and six academic institutes with a wide range of expertise in atmospheric physics. One focus of the development work is to address model shortcomings and deficiencies responsible for major model biases in the E3SM Atmosphere Model v1 (E3SMv1) including the substantially underestimated stratocumulus clouds, large regional precipitation biases over both land and ocean, and too strong Aerosol Indirect Effect (AIE) among others. Poor scale-awareness of model cloud parameterizations is also being addressed. Another focus is to enhance the capability of E3SM to simulate the climate response to scenarios of interest by implementing an interactive atmospheric chemistry in E3SM and improving the coupling of aerosols, atmospheric chemistry, and BGC. The development work will address the combined problems of scientific accuracy, scale-awareness, and computational efficiency."

Caption for the first image: "The proposed new physics shown in the dashed boxes will improve the current model (E3SM Atmosphere Model v1 – EAMv1) representation of atmospheric chemistry, aerosols, clouds, radiation, convection, and precipitation processes."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3693 on: August 25, 2020, 10:01:36 PM »
In financial circles managers follow the Precautionary Principle to reduce potential private financial losses while largely ignoring beneficial tail risks of outsized gains (see the first linked Wikipedia article on financial tail risk); however, in climate change politics decision makers tend to ignore disbenefit tail risks because they assume that this potential losses (and thus ignore the Precautionary Principle) will largely be carried by others.  As such, when the IPCC calculates our collective remaining Carbon Budget, they ignore fat tail projections of climate sensitivity and instead they also largely ignore mean and median projections of climate sensitivity & instead focus on mode projections (see the attached image).

However, I note that as MICI events have occurred numerous times in the paleorecord, the associated tail risk for such a future event is not a question of whether, but of when and how fast, this century.  The second linked Wikipedia article, indicates that by Kolmogorov's zero–one law either an MICI event will either happen, or not, this century and I note that MICI risks are self-organizing, or include strange attractors (and thus are not random) and that the risks of an MICI event this century are increasing for reasons including:

- The OHC of the Southern Ocean have been increasing since at least 1750.
- The Antarctic ozone hole has been promoting upwelling of the OHC storied in the Southern Ocean since the 1970s; and as the ozone hole has been recently healing itself its influence on westerly winds have been augmented by the parallel increase in GHG concentrations.
- The ice shelves in the ASE have been seriously degraded since at least the 1980s.
- If the CMIP6 Wolf Pack models are correct about TCR/ECS then GMSTA should increase more rapidly in coming decades; which will increase the coming risk of hydrofracturing.
- Super El Nino frequencies have been increasing and are projected to continue increasing, due to global warming.
- The Beaufort Gyre has already accumulated enough freshwater that a temporary reversal of its circulation direction would cause enough freshwater hosing to slow the MOC anytime from now to the coming decades.  Also, one CMIP6 model projects a seasonally (September) sea ice free Arctic Ocean by 2035; which could both flip the halocline and the Beaufort Gyre circulation.
- As GMSTA continues to increase the risk of a cascade of climate tipping points increases.


Title: "Tail risk"

https://en.wikipedia.org/wiki/Tail_risk

Extract: "Tail risk, sometimes called "fat tail risk," is the financial risk of an asset or portfolio of assets moving more than 3 standard deviations from its current price, above the risk of a normal distribution. Prudent asset managers are typically cautious with tail risk involving losses which could damage or ruin portfolios, and not the beneficial tail risk of outsized gains.
The common technique of theorizing a normal distribution of price changes underestimates tail risk when market data exhibit fat tails.
Tail risk is sometimes defined less strictly: as merely the risk (or probability) of rare events. The arbitrary definition of the tail region as beyond 3 standard deviations may also be broadened, such as the SKEW index which uses the larger tail region starting at 2 standard deviations."

&

Title: "Kolmogorov's zero–one law"

https://en.wikipedia.org/wiki/Kolmogorov%27s_zero%E2%80%93one_law

Extract: "In probability theory, Kolmogorov's zero–one law, named in honor of Andrey Nikolaevich Kolmogorov, specifies that a certain type of event, called a tail event, will either almost surely happen or almost surely not happen; that is, the probability of such an event occurring is zero or one.

Tail events are defined in terms of infinite sequences of random variables."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3694 on: August 26, 2020, 04:40:06 PM »
The linked reference provides more refined information about the pattern of the ocean heat content, OHC, and salinity, in the Southern Ocean; which does not bode well for the long-term stability of both sea ice and of ice shelves in the Weddell Sea (and adjoining) area(s):

Volker H. Strass, Gerd Rohardt, Torsten Kanzow, Mario Hoppema and Olaf Boebel (2020), "Multi-decadal warming and density loss in the deep Weddell Sea, Antarctica", J. Climate 01–60, https://doi.org/10.1175/JCLI-D-20-0271.1

https://journals.ametsoc.org/jcli/article/doi/10.1175/JCLI-D-20-0271.1/354273/Multi-decadal-warming-and-density-loss-in-the-deep

Abstract: "The world ocean is estimated to store more than 90 % of the excess energy resulting from man-made greenhouse gas driven radiative forcing as heat. Uncertainties of this estimate are related to under-sampling of the subpolar and polar regions and of the depths below 2000 m. Here we present measurements from the Weddell Sea that cover the whole water column down to the sea floor, taken by the same accurate method at locations revisited every few years since 1989. Our results show widespread warming with similar long-term temperature trends below 700 m depth at all sampling sites. The mean heating rate below 2000 m exceeds that of the global ocean by a factor of about five. Salinity tends to increase – in contrast to other Southern Ocean regions - at most sites and depths below 700 m, but nowhere strongly enough to fully compensate for the warming effect on seawater density, which hence shows a general decrease. In the top 700 m neither temperature nor salinity show clear trends. A closer look at the vertical distribution of changes along an approximately zonal and a meridional section across the Weddell Gyre reveals that the strongest vertically coherent warming is observed at the flanks of the gyre over the deep continental slopes and at its northern edge where the gyre connects to the Antarctic Circumpolar Current (ACC). Most likely, the warming of the interior Weddell Sea is driven by changes of the Weddell Gyre strength and its interaction with the ACC."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3695 on: August 26, 2020, 05:27:17 PM »
The linked reference about HadGEM3-GC3.1 projections related to climate responses from the modeled increasing Antarctic iceberg and ice shelf melt.  Key identified issues include that:
- Increased meltwater is increasing (temporarily) sea ice extent while reducing AABW production; both of which contribute to a slowing of the MOC.
- Increase snowfall at lower latitudes of Antarctica is applying more driving force on key marine glaciers; which will cause both ice velocities and iceberg calving to increase; and increased snow that falls directly into the ocean also contributes to both a slowdown of the MOC and increased advection of warm CDW towards key marine glacier grounding lines.

Shona Mackie; Inga J. Smith; Jeff K. Ridley; David P. Stevens and Patricia J. Langhorne (2020), "Climate response to increasing Antarctic iceberg and ice shelf melt, J. Climate 1–70; https://doi.org/10.1175/JCLI-D-19-0881.1

https://journals.ametsoc.org/jcli/article/doi/10.1175/JCLI-D-19-0881.1/353964/Climate-response-to-increasing-Antarctic-iceberg

Abstract: "Mass loss from the Antarctic continent is increasing, however climate models either assume a constant mass loss rate, or return snowfall over land to the ocean to maintain equilibrium. Numerous studies have investigated sea ice and ocean sensitivity to this assumption and reached different conclusions, possibly due to different representations of melt fluxes. The coupled atmosphere-land-ocean-sea ice model, HadGEM3-GC3.1, includes a realistic spatial distribution of coastal melt fluxes, a new ice shelf cavity parametrization and explicit representation of icebergs. This makes it appropriate to revisit how increasing melt fluxes influence ocean and sea ice, and to assess whether responses to melt from ice shelves and icebergs are distinguishable. We present results from simulated scenarios of increasing meltwater fluxes and show that these drive sea ice increases and, for increasing ice shelf melt, a decline in Antarctic Bottom Water formation. In our experiments, the mixed layer around the Antarctic coast deepens in response to rising ice shelf meltwater, and shallows in response to stratification driven by iceberg melt. We find similar surface temperature and salinity responses to increasing meltwater fluxes from ice shelves and icebergs, but mid-layer waters warm to greater depths and further north when ice shelf melt is present. We show that as meltwater fluxes increase, snowfall becomes more likely at lower latitudes, and Antarctic Circumpolar Current transport declines. These insights are helpful for interpretation of climate simulations that assume constant mass loss rates, and demonstrate the importance of representing increasing melt rates for both ice shelves and icebergs."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3696 on: August 26, 2020, 05:42:26 PM »
The linked article indicates that OHC of the Arctic Ocean below the halocline is increasing due to Atantification.

Title: "Growing underwater heat blob speeds demise of Arctic sea ice"

https://www.sciencemag.org/news/2020/08/growing-underwater-heat-blob-speeds-demise-arctic-sea-ice

Extract: "Ice has kept its grip on the Arctic with the help of an unusual temperature inversion in the underlying waters. Unlike the Atlantic or Pacific oceans, the Arctic gets warmer as it gets deeper. Bitter winters and chilly, buoyant freshwater from Eurasian rivers cool its surface layers, which helps preserve the underside of the ice. But at greater depths sits a warm blob of salty Atlantic water, thought to be safely separated from the sea ice.

As the reflective ice melts, however, it is replaced by darker water, which absorbs more of the Sun’s energy and warms. Those warming surface waters are likely migrating down into the blob, which robotic temperature probes, moorings, and oceanographic surveys show is steadily warming and growing. With enough heat to melt the Arctic’s ice three to four times over, the blob could devour the ice from below if the barrier of the cold surface layers ever dissipates.

Measurements from the eastern Arctic Ocean, published last week in the Journal of Climate, show the blob, usually found 150 meters below or deeper, has recently moved up to within 80 meters of the surface.  Increased turbulence means some of that heat is now melting ice, says Igor Polyakov, an oceanographer at the University of Alaska, Fairbanks. “This heat has become, regionally, the key forcing for sea ice decay.”

The process, called “Atlantification,” is already well underway in the Barents Sea, north of Norway, where fingers of warm Atlantic water have spread north and risen, melting sea ice even in winter months. The invasion shows no sign of stopping, says Helene Asbjørnsen, an oceanographer at the University of Bergen who has helped chart this migration. “Ultimately we expect it to extend into the Arctic more.”

See also:

Helene Asbjørnsen, Marius Årthun, Øystein Skagseth and Tor Eldevik (20 June 2020), "Mechanisms Underlying Recent Arctic Atlantification", Geophysical Research Letters, https://doi.org/10.1029/2020GL088036

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GL088036

Abstract
Recent warming and reduced sea ice concentrations in the Atlantic sector of the Arctic Ocean are the main signatures of ongoing Arctic “Atlantification.” The mechanisms driving the warming trends are nevertheless still debated, particularly regarding the relative importance of oceanic and atmospheric heat fluxes. Here, heat budgets along main Atlantic water pathways through the Barents Sea and Fram Strait are constructed to investigate the mechanisms of Atlantification during 1993–2014. The largest warming trends occur south of the winter ice edge, with ocean advection as the main driver. Warming in the marginal ice zone is mainly due to low surface heat loss from the 1990s to the mid‐2000s. In the ice‐covered northwestern Barents Sea, ocean advection and air‐sea heat fluxes act in concert to drive a gradual warming of the upper ocean. Despite a weakened stratification, no evidence is found of vertical oceanic temperature fluxes driving this upper‐ocean warming.

Plain Language Summary
Recent “Atlantification” of the Arctic is characterized by warmer ocean temperatures and a reduced sea ice cover. The Barents Sea is a “hot spot” for these changes, something which has broad socioeconomic and environmental impacts in the region. However, there is, at present, no complete understanding of what is causing the ocean warming. Here, we determine the relative importance of transport of heat by ocean currents (ocean advection) and heat exchanges between the atmosphere and the ocean (air‐sea heat fluxes) in warming the Barents Sea and Fram Strait. In the ice‐free region, ocean advection is found to be the main driver of the warming trend due to increasing inflow temperatures between 1996 and 2006. In the marginal ice zone and the ice‐covered northern Barents Sea, ocean advection and air‐sea heat fluxes are found to be of interchanging importance in driving the warming trend through the 1993–2014 period analyzed. A better understanding of the recent warming trends in the Barents Sea and Fram Strait has implications for how we understand the ocean's role in ongoing and future Arctic climate change.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

vox_mundi

  • Young ice
  • Posts: 4107
    • View Profile
  • Liked: 2399
  • Likes Given: 318
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3697 on: August 26, 2020, 10:04:33 PM »
Antarctica: 60% of Ice Shelves at Risk of Fracture, Research Suggests
https://amp.theguardian.com/world/2020/aug/26/antarctica-ice-shelves-risk-fracture-collapse

Approximately 60% of Antarctica’s ice shelves could be vulnerable to fracture, accelerating the loss of the Antarctic ice sheet and increasing sea-level rise, according to a paper.

A study published in the journal Nature has mapped areas where ice shelves hold back upstream ice and are susceptible to “hydrofracture”, where meltwater flows into crevasses and fissures in the ice and enlarges them, potentially triggering the collapse of the ice shelf.

This process could accelerate the loss of Antarctic ice more than some climatic models predict as atmospheric warming increases. The study follows scientists’ recent announcement that Earth has lost 28tn tonnes of ice from its surface since 1994.

Most climatic models do not include the impact of hydrofracturing in their calculations, although one 2016 paper did account for them in a simpler way than the new study.

https://www.nature.com/articles/nature17145

... Lai said: “We predicted that the ice-shelves areas that can collapse due to hydrofracture are mostly the crucial part of ice shelves that hold back the upstream flow of ice sheets. Thus the loss of these ice-shelf areas due to hydrofracture can substantially affect the flow of ice sheets into the ocean.


Areas of buttressing ice shelves that are vulnerable to hydrofracturing shown in red. Fractures in green and black areas should be stable; blue areas provide no buttressing. Boxes zoom in on two areas where surface meltwater is present today.

The recipe for hydrofracturing, of course, requires the “hydro” part—meltwater on the ice surface. That’s quite rare today.  Using a recent map of surface meltwater ponds on the East Antarctic Ice Sheet, which reaches lower (warmer) latitudes, the researchers find that only 0.6 percent of the ice shelf area there is both vulnerable and currently hosting meltwater. In the few notable areas with significant amounts of meltwater, fractures should be stable.

The problem is that projected warming of air temperatures could lead to much greater amounts of surface meltwater on the ice by the end of this century. And given the apparent vulnerability to hydrofracturing, that could mean more collapsed ice shelves like the Larsen B. There's also a lot more land ice behind these vulnerable sites, with bigger stakes for sea level rise.

https://arstechnica.com/science/2020/08/new-map-shows-vulnerability-of-antarctic-ice-to-self-fracking/

Ching-Yao Lai, et.al., Vulnerability of Antarctica’s ice shelves to meltwater-driven fracture, Nature 2020
https://www.nature.com/articles/s41586-020-2627-8
« Last Edit: August 26, 2020, 11:18:49 PM by vox_mundi »
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― Leonardo da Vinci

Insensible before the wave so soon released by callous fate. Affected most, they understand the least, and understanding, when it comes, invariably arrives too late

sidd

  • First-year ice
  • Posts: 5685
    • View Profile
  • Liked: 788
  • Likes Given: 0
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3698 on: August 27, 2020, 08:57:36 AM »
Thanks for the link to the Strass paper on weddell measurement of OHC. I shall have to read it carefully, in the light of the Hellmer projection of transition from cold to warm cavity under the ice shelf,

sidd

AbruptSLR

  • Multi-year ice
  • Posts: 18963
    • View Profile
  • Liked: 2078
  • Likes Given: 256
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3699 on: August 27, 2020, 03:43:27 PM »
The linked reference describes the results of a modeling investigation of decadal variations in ocean heat uptake can lead to a subsequent prolonged surge in GMSTA:

Bablu Sinha; Florian Sévellec; Jon Robson and A. J. George Nurser (2020), "Surging of Global Surface Temperature due to Decadal Legacy of Ocean Heat Uptake", J. Climate, 33 (18): 8025–8045,
https://doi.org/10.1175/JCLI-D-19-0874.1

https://journals.ametsoc.org/jcli/article/33/18/8025/345993/Surging-of-Global-Surface-Temperature-due-to

Abstract: "Global surface warming since 1850 has consisted of a series of slowdowns (hiatus) followed by surges. Knowledge of a mechanism to explain how this occurs would aid development and testing of interannual to decadal climate forecasts. In this paper a global climate model is forced to adopt an ocean state corresponding to a hiatus [with negative interdecadal Pacific oscillation (IPO) and other surface features typical of a hiatus] by artificially increasing the background diffusivity for a decade before restoring it to its normal value and allowing the model to evolve freely. This causes the model to develop a decadal surge that overshoots equilibrium (resulting in a positive IPO state), leaving behind a modified, warmer climate for decades. Water-mass transformation diagnostics indicate that the heat budget of the tropical Pacific Ocean is a balance between large opposite-signed terms: surface heating/cooling resulting from air–sea heat flux is balanced by vertical mixing and ocean heat transport divergence. During the artificial hiatus, excess heat becomes trapped just above the thermocline and there is a weak vertical thermal gradient (due to the high artificial background mixing). When the hiatus is terminated, by returning the background diffusivity to normal, the thermal gradient strengthens to prehiatus values so that the mixing (diffusivity × thermal gradient) remains roughly constant. However, since the base layer just above the thermocline remains anomalously warm, this implies a warming of the entire water column above the trapped heat, which results in a surge followed by a prolonged period of elevated surface temperatures."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson